Method for selecting an optimum access point in a wireless network on a common channel

ABSTRACT

The performance and ease of management of wireless communications environments is improved by a mechanism that enables access points (APs) to perform automatic channel selection. A wireless network can therefore include multiple APs, each of which will automatically choose a channel such that channel usage is optimized. Furthermore, APs can perform automatic power adjustment so that multiple APs can operate on the same channel while minimizing interference with each other. Wireless stations are load balanced across APs so that user bandwidth is optimized. A movement detection scheme provides seamless roaming of stations between APs.

FIELD OF THE INVENTION

[0001] The invention relates generally to wireless networks, and moreparticularly to wireless network configuration and power leveladjustment for network performance optimization.

BACKGROUND OF THE INVENTION

[0002] The proliferation of laptop and hand-held portable computers hasproduced a concomitant need for robust, reliable, and high performancewireless networks to maximize the mobility advantages of these devicesand increase the ease of construction and management of these wirelessnetworks. Current wireless networks, such as IEEE 802.11b, 802.11a,802.11g, (etc) networks, are subject to certain limitations that canlimit a mobile user's network performance and reliability. For instance,only a very limited number of radio channels are available. In thecurrent state of the art, wireless access points cannot effectivelyshare the same channel in the same area because of radio and controlprotocol interference. So, bandwidth over a given area is limited by thenumber of non-overlapping channels available. Also, current wirelessnetworks require manual site engineering to control the placement ofaccess points and channel distribution between access points, raisingthe cost and complexity of the wireless network installation process.Furthermore, user roaming between wireless access points isinconsistent. Once associated with an access point, a user will tend toremain associated with that access point even if another access point iscapable of providing higher performance for the user. It would bedesirable to provide wireless networking solutions which overcome theabove described inadequacies and shortcomings of current wirelessnetworks.

SUMMARY OF THE INVENTION

[0003] In accordance with the principles of the invention, variousapparatus, methods, and computer program products are provided toimprove the performance and ease of management of wirelesscommunications environments. For example, a mechanism is provided toenable access points (APs) to perform automatic channel selection. Awireless network can therefore include multiple APs, each of which willautomatically choose a channel such that channel usage is optimized.Furthermore, APs can perform automatic power adjustment so that multipleAPs can operate on the same channel while minimizing interference witheach other. Further aspects of the invention are used to cause loadbalancing of stations across APs so that user bandwidth is optimized.Novel movement detection schemes provide seamless roaming of stationsbetween APs. These and further aspects of the invention enable theprovision of automatically configurable, high performance wirelesscommunications environments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004]FIG. 1 shows a wireless communications environment in whichwireless users interact with other networked devices via an access point(AP).

[0005]FIG. 2 shows a wireless network in which wireless user devices, orstations (STAs), access the wireless network via an access point andshare the available network bandwidth.

[0006]FIG. 3 shows a wireless network wherein the stations access thenetwork via two separate access points.

[0007]FIG. 4 is a flow diagram representing how an AP builds a channelmap for use in an automatic channel selection scheme.

[0008]FIG. 5 is a flow diagram representing an automatic channelselection method.

[0009]FIG. 6 is a representation of a table kept by APs for use in analternate channel selection scheme.

[0010]FIG. 7 is a flow diagram representing an alternate automaticchannel selection scheme.

[0011]FIG. 8 is a flow diagram representing a preferred embodiment of anautomatic channel selection scheme.

[0012]FIG. 9 is a representation of a Scan Table kept by APs for use inthe automatic channel selection scheme of FIG. 8.

[0013]FIG. 10 is a representation of a Channel Map kept by APs for usein the automatic channel selection scheme of FIG. 8.

[0014]FIG. 11 is a representation of a Triplet Channel Map kept by APsfor use in the automatic channel selection scheme of FIG. 8.

[0015]FIG. 12 is a representation of a Claim APs table kept by APs foruse in the automatic channel selection scheme of FIG. 8. FIG. 13 is aflow diagram showing how an AP builds an AP KnownAPs table.

[0016]FIG. 14 is an example of an AP KnownAPs table maintained by an AP,and used for power adjustment.

[0017]FIG. 15 is a flow diagram representing the process by which an APbuilds an AP AssociatedSTA table, for use in load balancing.

[0018]FIG. 16 is an example of an AP AssociatedSTA table.

[0019]FIG. 17 is a block diagram representing a general mechanism bywhich an AP adjusts its transmit power backoff.

[0020]FIG. 18 is a block diagram representing a preferred embodiment ofthe transmit power backoff mechanism of FIG. 13.

[0021]FIG. 19 is a table showing expected standard errors related tonumber of power level samples.

[0022]FIG. 20 is a flow diagram representing the process by which an APadjusts its transmit power backoff during STA movement.

[0023]FIG. 21 is a flow diagram representing an AP auction process, usedfor load balancing of STAs across APs.

[0024]FIG. 22 is a flow diagram representing the AP's handling of bidsduring the auction.

[0025]FIG. 23 is a flow diagram representing the STA initializationprocess.

[0026]FIG. 24 is a flow diagram representing a general mechanism bywhich a STA in a wireless communications environment canvasses channels.

[0027]FIG. 25 is a flow diagram representing the preferred embodiment ofFIG. 20 as implemented in an 802.11 wireless networking environment.

[0028]FIG. 26 is an example of a STA Known APs table, used by STAs forpower adjustment and load balancing.

[0029]FIG. 27 is a flow diagram representing the process by which theSTA Known APs table is built by a STA.

[0030]FIG. 28 is a flow diagram representing the STA power adjustmentprocess.

[0031]FIG. 29 is a flow diagram representing the STA Bidding process.

[0032]FIG. 30 is a flow diagram representing the process by which a STAcalculates corrected distances for use in determining whether to bid foran AP.

[0033]FIG. 31 is an example of a distance_to_rate table for use in an802.11 wireless networking environment.

[0034]FIG. 32 is an example of a rate_to_load table for use in an 802.11wireless networking environment.

[0035]FIG. 33 is a flow diagram representing the STA Bidding process inmore detail.

[0036]FIG. 34 is a flow diagram representing the process by which a STAdetects its own movement.

[0037]FIG. 35 is a block diagram showing the software architectures ofAPs and STAs.

[0038]FIG. 36 is a more detailed block diagram of the softwarearchitecture of an AP implementing the invention in an 802.11 wirelessnetworking environment.

[0039]FIG. 37 is a more detailed block diagram of the softwarearchitecture of a STA implementing the invention in an 802.11 wirelessnetworking environment.

[0040]FIG. 38 represents the encoding of a DRCP (Dynamic Radio ControlProtocol) message in an 802.11 beacon frame.

[0041]FIG. 39 represents the encoding of a DRCP message in an 802.11data frame.

[0042]FIG. 40 is a table summarizing the DRCP messages used in thevarious aspects of the invention.

[0043]FIG. 41 is a table describing the various fields used in DRCPmessages.

[0044]FIG. 42 is a diagram of the message format of a DRCP Preclaimmessage.

[0045]FIG. 43 is a diagram of the message format of a DRCP Claimmessage.

[0046]FIG. 44 is a diagram of the message format of a DRCP Announcemessage.

[0047]FIG. 45 is a diagram of the message format of a DRCP Bid message.

[0048]FIG. 46 is a diagram of the message format of a DRCP Acceptmessage.

[0049]FIG. 47 is a diagram of the message format of a DRCP RegistrationRequest message.

[0050]FIG. 48 is a diagram of the message format of a DRCP RegistrationAcknowledge message.

[0051]FIG. 49 is a graph showing discrete measurements of received powerover time from the perspective of a wireless network user.

[0052]FIG. 50 is a graph showing discrete measurements of received powerover time from the perspective of a wireless network user, and showingthe estimated average received power for the user within a 99%confidence interval.

[0053]FIG. 51 is a graph similar to FIG. 3 showing two differentestimated average received power measurements for small sample sizes andtheir 99% confidence intervals.

[0054]FIG. 52 is a graph showing two different estimated averagereceived power measurements and their 99% confidence intervals, one fora large sample size and one for a small sample size.

[0055]FIG. 53 is a graph showing a long term average measurement and ashort term average measurement with 99% confidence interval, thecomparison showing that it can be determined that a user has moved.

[0056]FIG. 54 is a table showing the number of samples that need to betaken in order to cause the long term average confidence interval rangeto converge toward zero.

[0057]FIG. 55 is a flow diagram of the general operation of the methodof the invention.

[0058]FIG. 56 is a block diagram of an embodiment of a wireless networkin which the invention is deployed, wherein an AP ascertains that a userhas moved.

[0059]FIG. 57 is a block diagram of an alternate embodiment of theinvention, wherein a user ascertains that the user has moved.

[0060]FIG. 58 is a block diagram of one embodiment of the inventionemploying ring buffers.

[0061]FIG. 59 is a block diagram of an alternate embodiment of theinvention employing batched means.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0062] In accordance with the present invention, a fully automaticcontrol system is provided for wireless communications environments.Referring to FIG. 1, a typical wireless communications environment 10includes access devices 12 (one shown) that interface between a wiredcommunications medium 14 and wireless devices 16 to provide networkaccess to the wireless devices 16. Wireless devices 16 can thuscommunicate with wired devices 18 and with each other via the accessdevice 12. These access devices 12 are referred to by various namesdepending upon the wireless architecture employed, and are hereinreferred to as “access points” or “APs”. The wireless devices 16 alsohave various architecture dependent names and are herein referred to as“stations” or STAs. A wireless communications capable device may be anAP, or a STA, or both.

[0063] Various types of wireless communications environments 10 exist.Wireless communications environments include for example wireless datanetworks and wireless I/O channels. An example of a wireless datanetwork is described in “IEEE Standard for Informationtechnology—Telecommunications and information exchange betweensystems—Local and metropolitan area networks—Specific requirements—Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)specifications—Amendment 1: High-speed Physical Layer in the 5 GHzband”, incorporated herein by reference(hereinafter “802.11”).Furthermore, various different 802.11 “modes” are defined. For example,in IEEE 802.11 compatible wireless networks, wireless devices may bearranged in an “infrastructure mode”, whereby the network is configuredsuch that STAs 16 communicate with other network devices via an AP 12,as shown in FIG. 1. 802.11 compatible devices may also be arranged in“ad-hoc” mode, whereby all the STAs 16 are within transmission range andcan communicate directly with each other. Furthermore, wireless “mesh”technologies exist, whereby each wireless device acts as both an AP anda STA. Wireless I/O channels can be used to provide I/O communications,for example, between servers and storage devices via the “Bluetooth”Standard, or between home entertainment audio and video components, orbetween wireless telephone handsets and base stations. The variousaspects of the invention apply to generally to wireless networkingarchitectures, including those used in wide area networks, metropolitanarea networks, enterprise networks, and home networks, and wireless I/Ochannel architectures, as they exist now and as they are developed.

[0064] According to aspects of the invention, an arbitrary number ofwireless access points (APs) can be placed in arbitrary positions, andall APs and STAs will automatically configure themselves for optimalchannel usage, power levels, and STA/AP associations. So, in a wirelessnetworking environment, channel usage is optimized while interferencebetween APs is minimized. Wireless devices such as wireless enabledlaptops or hand-held computing devices or Internet protocol telephones,are transparently and seamlessly distributed between APs such thatnetwork performance is optimized from the perspective of the user of thewireless device. And, in a wireless I/O channel environment that mightbe employed for example in a home, audio, video, and other appliancesmay be moved without performance degradation, and channel usage for eachappliance may be optimized so that the appliances do not interfere witheach other.

[0065] In order to expedite the understanding of the invention, certainexamples will be described as they apply to the relatively well known802.11 wireless LAN architecture, with the understanding that theprinciples of the invention apply more generally to any wirelesscommunications environment. A preferred implementation of the inventiveprinciples will then be described as embodied in an 802.11 wirelessnetwork

[0066] The following aspects of the invention contribute to itsadvantages, and each will be described in detail below.

[0067] 1. AP Initialization: In many wireless communicationsenvironments, multiple frequencies (“channels”) are available for use byAPs. For example, in accordance with 802.11b and 802.11 g, 3non-overlapping channels are available. In accordance with IEEE 802.11a,13 non-overlapping channels are available. In an environment wheremultiple APs are employed, it will be seen that it is advantageous forthe APs to use different channels to optimize performance and minimizeinterference. In accordance with the invention, APs perform automaticchannel selection. Where multiple APs are distributed in a given area,the APs execute a distributed protocol to pick channels for each AP. APsclose to each other use non-overlapping channels.

[0068] 1. AP Optimization:

[0069] a. Power Adjustment: When the number of APs in a wirelesscommunications environment exceeds the number of non-overlappingchannels, APs and STAs adjust their power such that APs and STAs on thesame channel can co-exist in an area without interference. For APs usingthe same channel, APs continually re-adjust their power levels based onenvironmental factors such as signal strength changes due to movement ofdoors, people, background noise floor, and the like, so that the users'optimal bandwidth is maintained without undue interference.

[0070] a. Auction: APs keep track of various parameters for STAs thatare associated with them, and STAs will roam between APs for loadbalancing purposes, which can help to maximize performance over a groupof STAs.

[0071] 1. STA initialization: STAs associate with an initial AP.Invention enabled STAs turn on functions that allow them to receivemessages from invention enabled APs.

[0072] 1. STA optimization:

[0073] a. Channel Canvassing: In order to further optimize performance,STAs periodically canvass the other channels in the band in which theSTA is operating to see if a “better” AP is present. To ascertainwhether another AP is “better”, various parameters are considered, suchas signal strength and load factors, to be further described.

[0074] a. Bidding: If a better AP is found, a STA enters a biddingprocess to try to cause the STA to roam to the better AP. Load balancingis thereby achieved. In addition, the bidding process accommodates STAmovement by causing the STA to associate to a better AP after it hasmoved closer to the better AP.

[0075] a. Power Adjustment: STAs perform power adjustment such that theycan maintain throughput to and from their currently associated AP whileminimizing the interference with nearby wireless devices that may beusing the same channel.

[0076] a. Movement Detection: STAs perform movement detection so thatthe bidding process can be turned off while a STA is moving, and thenturned back on when the STA has stopped moving. When turned back on, a“better” AP may turn up and thus the STA will bid for it.

[0077] 1. Software Architecture

[0078] a. The above functionality is advantageously implemented in APsand STAs in a modular manner for ease of transfer between platforms.

[0079] a. The above functionality is described in detail as it isimplemented in a preferred 802.11 network embodiment.

[0080] 1. Movement Detection statistical analysis: A novel scheme forhighly accurate and computationally efficient detection of a change inan attribute subject to high noise variation is described, and appliedto detection of the movement of wireless STAs.

[0081] Since exemplary examples will refer to the 802.11 networkingenvironment, the following information provides relevant context, whileunderstandably not limiting the invention to 802.11 environments.

[0082] In an 802.11 network, APs periodically send frames called“Beacons”. STAs listen for Beacons. When an unassociated STA (i.e. a STAthat is not yet able to communicate on the wireless network) hearsBeacons at what it deems to be a reasonable power level, it can attemptto authenticate with the AP sending the Beacons, and then associate withthat AP. Once authenticated and associated, the STA is able to send dataframes to other STAs on the wireless network via the AP. Moreparticularly, APs and STAs send and respond to three different types offrames, known as Class 1 Frames, Class 2 Frames, and Class 3 Frames.Class 1 Frames include control frames and management frames, and can besent regardless of whether a STA is authenticated and associated with anAP. A Beacon is a type of Class 1 frame. Class 2 Frames are sent onlyonce a STA is authenticated, and include for example associationrequest/response messages. Class 3 Frames can be sent only ifassociated, and include data frames.

[0083] In order to maximize user bandwidth and throughput, the inventionautomatically optimizes the operation of multiple APs for a givenwireless communications environment. In accordance with the exemplaryIEEE 802.11 a networking standard, 13 non-overlapping frequencies areavailable for use by the APs. Each AP is capable of transmitting andreceiving data at a maximum rate of 54 Mbps. The actual rate at whichdata is transmitted and received between an AP and a STA depends uponmany factors, including the distance between the AP and the STA, thestructures located between the AP and the STA, and the environmentalinterference occurring on the particular frequency. One skilled in theart will realize that the invention is not limited by the maximum datarates of current wireless technology, nor is it limited by currentlyunderstood radio frequency attenuation factors. The principles of theinvention will continue to be applicable as wireless technology evolves.

[0084] Consider an area such as the wireless network shown in FIG. 2,wherein 8 users (shown as STAs 16), which may be mobile laptops, PDAs,and the like, share a space including a single AP 12 operating on one ofthe 13 available 802.11a frequencies, denoted “f1”. The 8 users 16 sharethe bandwidth provided by the AP 12. If all 8 users 16 are located closeenough to the AP such that the AP provides a 54 Mb bit maximum datarate, then all 8 users 16 share the AP's bandwidth such that each usermaintains 6.75 Mb throughput on average. (The invention contemplates thefact that data traffic is bursty and that a user in the present examplemay attain 54 Mb throughput for a short interval, but for purposes ofsimplicity, the average throughput over time for a given user isdiscussed.)

[0085] Now, referring to FIG. 3, a second AP 12 has been added in thearea. The second AP 12 operates on a different one of the 13frequencies, denoted “f2”, such that the two APs 12 do not interfere,nor do their associated STAs 16. As shown, 4 of the 8 users have roamedto the second AP 12. Now each user maintains 13.5 Mb throughput onaverage. Addition of further APs on different frequencies furtherincreases user average throughput.

[0086] In accordance with the invention, a Dynamic Radio ControlProtocol (DRCP) provides a mechanism for an arbitrary collection of STAsand APs to automatically control the frequency and power of their radiosin order to extend the properties exemplified in FIG. 2 to maximizeoverall system performance. DRCP messages are passed between APs andAPs, as well as between APs and STAs to implement this functionality.Eight types of messages are used: DRCP Preclaim, DRCP Claim, DRCPAnnounce, DRCP Bid, DRCP Accept, DRCP Registration Request, and DRCPRegistration Acknowledge.

[0087] DRCP Preclaim and Claim messages are exchanged between APs duringAP initialization, and are used to aid automatic channel selection inaccordance with the invention. DRCP Announce messages are sent by APsand received by STAs during STA optimization. These Announce messagesinform invention-enabled STAs of available invention-enabled APs towhich they may choose to associate, and provide information about APsthat STAs can use to aid a decision as to whether to request to roam toanother AP. DRCP Bid messages are sent by STAs to APs during STAoptimization. These messages inform invention-enabled APs ofinvention-enabled STAs that are requesting association to the APs. DRCPAccept messages are sent by APs to STAs in response to DRCP Bidmessages. These messages inform a STA that it may associate with the APit is requesting to associate with. DRCP registration request andacknowledge messages are exchanged by invention-enabled APs and STAs toindicate to each that the other is DRCP capable.

[0088] The DRCP protocol employing these messages will first bedescribed as used in a generic wireless communications environment. Thedetailed implementation of each of these messages will then be furtherdescribed in terms of a preferred embodiment in an 802.11 environment.

[0089] The aspects of the invention are now described as they apply toAP initialization and optimization, and then as they apply to STAinitialization and optimization. It is noted that, though many of theinventive aspects described herein with regard to STAs and APs areadvantageous when implemented, they are not required to be implementedin a wireless communications environment. Performance advantages areachieved when only the APs, or only the STAs, or both implement one ormore of the various aspects of the invention.

[0090] 1. AP Initialization

[0091] During AP initialization, APs perform automatic channelselection. In accordance with the channel selection aspect of theinvention, APs located in the same wireless network automatically selectchannels for operation such that they do not interfere with nearby APs.The invention contemplates that different bands of frequencies areavailable, for example based on 802.11 version and the country in whichthe network is deployed. According to a preferred embodiment, APsattempt to select a channel, in each band in which the AP is equipped tooperate, which is least likely to interfere with other APs that arealready deployed. APs also quarantine channels in accordance with rulesassociated with regulatory domains (Europe, etc.) so they don'tinterfere with other wireless applications (radar, etc.). In the eventthat one AP selects a free channel, and another AP selects the same freechannel at the same time (i.e. a channel selection “Collision”), theAPs' media access control (MAC) addresses are used as a tie breaker. Ifthe other AP is a standard AP that does not include the improvementsassociated with the current invention, then the invention-enabled APwill direct its own radio to the “next best” channel. The AP repeats thechannel selection phase for each band of frequencies.

[0092] More particularly, referring to FIG. 4, before a newly added AP12 starts to “Beacon” (i.e. broadcast management packets to other APsand STAs), the AP 12 first examines a list of RF bands supported by theAP 12, and the list of channels supported and not quarantined by theradio which implements the Physical Layer (PHY) for each RF band. The AP12 then selects a channel in each band according to the followingalgorithm:

[0093] For each band:

[0094] Scan Intervals occur periodically. During a Scan Interval (step20), the AP 12 passively scans all channels which the AP supports withinthe band (step 22). The AP 12 gathers a list of active APs 12, thechannels on which they are operating, and the power at which the beaconsfrom each AP 12 was heard. This information is used to build a tablecalled a channel map 24 (step 26), which contains a list of all APs 12heard from, the channel on which they were heard, and the signalstrength at which they were heard. There is a separate channel map 24for each band. The AP 12 sorts the channel map to produce a list of APs12 in ascending order of power level (step 28).

[0095] Referring to FIG. 5, a channel is now selected by the AP 12 asfollows. First, the AP 12 peruses the channel map (step 30), and ifthere is a channel on which no AP 12 is operating (i.e. signalstrength=0) (step 32), then the AP 12 selects that channel (step 34).Otherwise, the AP 12 peruses the list for the channel transmitting theweakest signal (step 36). The AP 12 now enters a time interval referredto as the “claiming period” (step 38).

[0096] If the AP 12 selected a channel having the weakest signalstrength, the AP 12 notes the channel-ID of the channel that it hasselected, the received power level on the channel, and the AP-ID of theAP that generated that power level (step 40). It will use the powerlevel value as a baseline against which to detect increases in receivedpower on its selected channel. If the AP 12 selected an empty channel,the baseline power level will be the AP's noise floor.

[0097] The AP 12 then advertises its intention to use the selectedchannel by periodically transmitting DRCP Claim messages during theclaiming period (step 42). Claim messages are transmitted at full power.During this claiming period, the AP 12 receives all Beacons, DRCP Claimmessages, and DRCP Announce messages transmitted on the currently chosenchannel (step 44) and uses the information contained therein to build an“Other APs” table 46 (FIG. 6, FIG. 5 step 48). For each Beacon itreceives, the AP 12 notes the AP-ID and the received power level in theOther APs table 46. For each Claim or Announce message it receives, theAP 12 notes the AP-ID of the AP that sent the message, the receivedpower level, and the transmit power backoff (TP backoff) in the OtherAPs table 46. The TP Backoff value indicates how far from maximum powerthe sending AP's radio has been turned down, and will be explained inmore detail in the AP Power Adjustment section. The AP 12 also marks theentry for that AP-ID as being DRCP capable. A normalized received powervalue is calculated by adding the TP Backoff value to the received powervalue. The normalized received power value equalizes the AP power levelsfor comparison purposes. When the AP 12 receives a Beacon or DRCPmessage from an AP for which it already has an entry, it updates theentry and stores the received power and TP_backoff values as a list.

[0098] If another AP 12 starts to radiate significant energy on theselected channel, one of two events must have occurred. The new AP 12 iseither not running DRCP, or a conflict has occurred with anotherDRCP-active AP, where a race condition has caused the other DRCP-activeAP to select the same channel at the same time. This is called a ChannelSelection Collision (CSC).

[0099] At the end of the claim period (step 50), the AP 12 stops sendingClaim messages and evaluates the information it has collected, its CSCdata, to determine if a CSC has occurred. It looks to see if thereceived power in any entry is greater than the baseline power level itrecorded for the channel (step 52). If so, it looks to see if thereceived power is exceeded in at least half of the power level valuesfor the entry (step 54). If so, the AP 12 checks to see whether the APin the entry is DRCP capable (step 56).

[0100] If the other AP is not DRCP active, the AP 12 defers to thenon-DRCP-active AP and starts the entire channel selection process overagain.

[0101] If the other AP is DRCP-active, then a CSC is assumed to haveoccurred. When a CSC has occurred, the MAC address of the other AP iscompared to the MAC Address of this AP 12. If the MAC address of this AP12 is numerically higher than the observed MAC address (step 58), thisAP 12 starts the channel selection process over again.

[0102] If at the end of the claiming period, the AP has succeeded inclaiming the selected channel, it begins running on the channel. The APstarts beaconing, begins sending DRCP Announce messages, and prepares toenter the Optimization stage in order to run its Auction and PowerAdjustment functions (step 60).

[0103] A variation on the channel selection process of FIG. 5 can beemployed to improve channel selection coverage when several APs 12 arepowered on all at once. Referring to FIG. 7, each AP, upon power-up,sends a claim message on a first channel chosen from the channel map-forpurposes of example designated channel 1 (steps 62, 64). All APs scanall channels. All APs scanning on channel 1 will hear each other's claimmessages. During the claiming period, an AP will ascertain whetherchannel 1 is in fact available for use by it. Accordingly, the APlistens for other DRCP Claim messages on the same channel, which wouldindicate that another invention-enabled AP is trying to use the samechannel (step 66). The AP 12 keeps track of the number of different APsit hears (based on AP IDs the claim messages received) and the averagesignal strength of claim messages from each AP. The AP 12 builds anadjacency vector (adjacency count, adjacency power total) (step 68).Adjacency count represents the number of APs heard on the channel.Adjacency power total represents the sum of the average power levels foreach AP heard. Each AP sends its adjacency vector to all the other APsin its claim messages step 70. If a DRCP claim message is received (step72), in this case on channel 1, the AP 12 first compares its adjacencycount with the adjacency count received in the claim message (step 74).If the AP 12's adjacency count is higher than that received in the claimmessage, this probably indicates that the AP 12 is closer to the centerof the network. The AP 12 therefore continues to claim the channelduring the claim period. If the AP's adjacency count is the same as theadjacency count received in the claim message (step 76), the AP 12 thencompares its own adjacency total power to the adjacency total powervalue received in the claim message. If the AP 12's own adjacency totalpower is higher than that received in the claim message (step 78), thismay also indicate that the AP 12 is closer to the center of the network,and therefore the AP 12 continues to send claim messages on the channel.If the AP 12's own adjacency total power is the same as that received(step 80), then the AP 12 performs the previously described MAC addresstest step 82). If the AP 12 finds that its own adjacency count oradjacency power are lower than any received in claim messages, or thatin the event of a tie on these values that its MAC address is higher, itceases to send claim messages on the channel and returns to peruse thechannel map (step 84). Otherwise, the AP 12 continues to send claimmessages including its adjacency vector (step 70). If, at the end of theclaiming period (step 86), the AP 12's adjacencies are greater thanother AP's adjacencies, the AP 12 has won the channel and proceeds tothe AP optimization phase (step 88). According to this method, the APsclosest to the center of a multi-AP network obtain the first channelassignments and subsequent channels are assigned to the other APs.

[0104] Referring to FIG. 8, a preferred embodiment of the automaticchannel selection algorithm is shown. For each band:

[0105] Scan Intervals occur periodically. During a Scan Interval (step100), the AP 12 scans all channels which the AP supports within theband, receiving Beacons and Announce messages (step 102). Theinformation received in the Beacon and Announce messages is used tobuild a table called the “Scan table” (step 104). An example of a Scantable 106 is shown in FIG. 9. The Scan table 106 includes an entry foreach AP 12 from which a Beacon or Announce message has been received.For each entry, there is stored the AP-ID and the channel on which thatAP 12 was heard. Also stored is a “rxPowerRunningTotal” value thatrepresents the sum of the signal strengths of each message received fromthat AP 12. Also stored is a “rxPowerSampleCount” value that representsthe number of messages received from the AP 12. A DRCP flag is set if anAnnounce message has been received from the AP 12. The entryAge entry isincremented every time the channel is scanned. The “rxPowerAvg” iscalculated during a Preclaim interval as will be further described.

[0106] As the scan progresses, the rxPowerSampleCount values in the Scantable 106 are monitored, and if any one of them exceeds a threshold,herein labeled “threshold1” (step 108), the AP 12 proceeds to step 110to build a channel map. In addition, if any entryAge value in the tableexceeds a certain threshold “threshold2” (step 112), the AP 12 willproceed to step 110. Also, if the number of scans completed exceeds acertain threshold “threshold3” (step 114), the AP 12 will proceed tostep 110. Otherwise the AP 12 continues scanning and updating the Scantable 106.

[0107] An example of a preferred channel map 116 is shown in FIG. 10.The channel map 116 contains an entry for each channel ID. To build thechannel map, the AP 12 peruses the Scan table 106 and calculates the“rxPowerAvg” value for each entry, as:

RxPowerAvg[I]=Scan table[i].rxPowerRunningTotal/Scantable[i]rxPowerSamplecount;

[0108] For each channel, the AP-ID with the highest rxPowerAvg value isentered in the channel map 116. The AP's rxPowerAvg value is enteredinto the channel map 116 as the highestPwrlevel parameter.

[0109] In certain network implementations, it is undesirable to locatetwo operating APs 12 within a certain distance of each other, becausedoing so does not increase network performance and may reduce it. So,according to a preferred option, once the channel map has beenassembled, the AP 12 checks the channel map to see if any of thehighestPwrlevel values in the map exceed a certain threshold power level(step 118). The threshold power level is chosen to indicate that the AP12 is located too close to another AP. If any highestPwrlevel exceedsthe threshold power level, the AP 12 is placed in “Standby mode” (step120). The AP 12 in Standby mode waits for a period of time hereinreferred to as “Standby Interval” before returning to start another scaninterval (step 122).

[0110] If no highestPwrlevel values are found to exceed the thresholdpower level, the AP proceeds to assemble a triplet channel map 124 (step126). As shown in FIG. 11, the AP 12 sorts a channel map into triplets,for example, channels 1, 2 and 3, channels 2, 3 and 4, channels 3, 4 and5, etc.. The power heard on each channel in the triplet is averaged intoa triplet average. The list of triplets is sorted in ascending order,with the triplet with the lowest average power at the top of the list.The AP 12 starts at the top of the list and looks for the first tripletin which the power heard on the center channel of the triplet is lessthan or equal to the power heard on the two adjacent channels, andselects this channel (step 128). If no such triplet is available, the APselects the channel with the lowest triplet average. In the exampleshown in FIG. 11, AP 12 chooses channel 3. This process advantageouslyminimizes interference between channels by selecting channels that donot tend to have high power adjacent channel usage.

[0111] The AP 12 then records the baseline power for the selectedchannel as the highestPwrlevel value for the channel, and records theAP-ID of the AP at that power level (step 130). A Preclaim Interval isnow entered (step 132). During the Preclaim interval, the AP transmitsPreclaim messages on the selected channel (step 134). The AP 12 alsoreceives Beacon, Announce, and Preclaim messages on the channel (step136). The AP 12 uses the received messages to update the Scan table(step 138). The AP 12 continues to update the Scan table until one oftwo Preclaim intervals expires. During the min Preclaim interval (step140), the rxPowerSampleCount value for each AP-ID on the selectedchannel is checked to see if a minimum sample size threshold has beenexceeded. If so, the Preclaiming interval ends and the AP proceeds tocheck to see whether too many APs are operating on the selected channel(step 142). Otherwise, the Preclaiming period extends until the end ofthe max Preclaim interval (step 144).

[0112] In some network environments, and in particular environments oflimited area, the operation of too many APs on the same channel does notincrease network performance and may cause a performance reduction. So,according to a preferred option, the AP checks to see if there are toomany APs operating on the network (step 142). The number of differentAP-IDs present in the Preclaim APs table is used to make thisdetermination. If there are too many APs operating on the selectedchannel at a power level greater than a defined threshold, the AP 12enters Standby mode

[0113] If there are not too many APs operating on the selected channel,the AP 12 calculates an “adjacency vector sum” (step 146). The adjacencyvector sum is calculated over all APs on all channels as:

Adjacency vector sum=sum(Preclaim APs[i].ReceivedPowerTotal/PreclaimAPs[i].count)

[0114] The adjacency vector sum is used as a tiebreaker if necessaryduring the Claiming interval, to be further described.

[0115] The AP 12 now enters the Claiming interval (step 148). During theClaiming interval, the AP 12 transmits Claim messages on the selectedchannel (step 150). Claim messages include the adjacency vector sum. TheAP 12 also receives all Beacon, Announce, and Claim messages on theselected channel (step 152). The AP 12 uses the information contained inthe received messages to build a “Claim APs table” 154 (step 156). Anexample of the Claim APs table is shown in FIG. 12. The Claim APs table154 contains an entry for each AP-ID. The received power level of eachmessage received from a given AP is stored in the Claim APs table 154 asa list of values (shown as column “ReceivedPowerlevel). Furthermore, foreach Announce or Claim message received, a DRCP flag is set. The APcontinues to update the Claim APs table until the end of the Claiminginterval (step 158).

[0116] The AP 12 then evaluates the Claim APs table 154 (step 160) toascertain whether any other APs were heard from. If no entries exist inthe Claim APs table 154 (step 162), the AP 12 has “won” the selectedchannel. The AP 12 can then begin Beaconing and sending Announcemessages on the channel (step 164). If the Claim APs table 154 includesone or more entries, then if the selected channel was empty at thebeginning of the Claiming Interval (step 166), the AP 12 concedes thechannel and returns to re-scan (step 100). Otherwise, if the channel wasnot empty, then if the ReceivedPowerlevel values for all entries in thetable are less than the baseline level recorded during Preclaiming plusa threshold level (e.g. 2 db) (step 168), then the AP has won thechannel (step 164). However, if the AP does find a ReceivedPowerlevelvalue that exceeds the baseline power level plus the threshold level,and that entry is associated with an AP-ID that was not the one recordedon the channel during the Preclaiming Interval, then the AP checks theentry's DRCP flag (step 170). If the DRCP flag indicates that the AP-IDassociated with the entry is not DRCP capable, then the AP returns backto the scan interval to re-start the channel selection process. If theDRCP flag indicates that the APID associated with the entry is DRCPcapable, then the AP compares its adjacency vector with the adjacencyvector received in the other AP's claim messages (step 172). If the AP'sadjacency vector is less than the other AP's adjacency vector, the APconcedes the channel and returns to re-scan. If the AP's adjacencyvector is not less than the other AP's adjacency vector, then the APchecks to see if the adjacency vectors are equal (step 174). If theyare, the MAC addresses of the two APs are compared (step 176). If theAP's MAC address is greater than the other AP's MAC address, the AP has“won” the channel (step 164). Otherwise, the AP concedes the channel andreturns to re-scan (step 100). One skilled in the art will realize thatthe MAC address comparison decision is arbitrary and can be made in theopposite manner.

[0117] 1. AP Optimization Once an AP is running on a channel, itcontinuously performs the following functions to optimize itsconfiguration in the wireless LAN:

[0118] Radio Power Adjustment. Each DRCP-enabled AP adjusts its power asappropriate, to accommodate the nearest AP operating on its channelwhile maintaing its connection to its farthest associated STA. The APconveys a TP_backoff parameter in its Announce messages. The TP_backoffvalue provides an indication of how far the sending AP has turned itstransmit radio down. This TP_backoff value is used by other APs todetermine their own TP_backoff values. A STA that is associated to theAP can then adopt the communicated TP_backoff value to adjust its radiopower, and can track this value as it changes.

[0119] Auction. The AP runs the Auction process to accept new DRCP STAsfor association, as appropriate, based on received DRCP Bid messages.These two functions are now described in terms of a preferredembodiment.

[0120] 2.a. Radio Power Adjustment

[0121] 2.a.1 AP maintained tables

[0122] In order to perform Radio Power Adjustment, the AP 12 maintains anumber of tables. The tables include information received from other APsand STAs operating on the selected channel. This information is used toascertain such things as power levels of other devices on the channel,and distances between devices on the channel, in order to control theAP's power level.

[0123] 2.a.1. AP KnownAPs table

[0124] Each AP 12 maintains a number of tables that it consults toperform power adjustment. One such table is the AP KnownAPs Table 200.As shown in FIG. 13, once initialized on a channel, an AP 12 receivesBeacons and DRCP Announce messages from all other APs 12 operatingwithin the range of its radio, on its channel (steps 202, 204, 206). TheAP 12 uses these received messages to build the AP KnownAPs table 200.For each message it receives, the AP 12 checks to see if it has an entryin the AP knownAPs table for the AP-ID in the message (step 208). Iffound, the AP 12 updates the entry (step 210), otherwise it creates anew one (step 212), up to a maximum of Max_APs entries (step 214). Thevalue of Max_AP is design dependent.

[0125] Referring to FIG. 14, the AP 12 stores the following fields inthe corresponding AP knownAPs table 200 entries:

[0126] AP-ID

[0127] TP Backoff

[0128] Max Power

[0129] DRCP capable

[0130] Age

[0131] Normalized power

[0132] Sample size

[0133] Corrected power

[0134] The AP-ID, TP Backoff, and Max Power fields are extracted fromeach DRCP Announce and Hello message received. The TP Backoff value isstored as a list of values for each message received from each AP-ID.The sample size is the number of TP Backoff values received for eachAP-ID. Since Announce messages are only sent by DRCP-enabled APs, the AP12 also marks the entry as DRCP-active. APs sending Beacons whichcontain no DRCP fields are not marked DRCP-active. For each messagereceived, the AP adds the TP Backoff value to the received power levelto determine a normalized received power level, as follows:

normalized_power=avg(received_power+tp_backoff);

[0135] Accounting for the TP backoff in the normalized power levelprovides a value that is consistent and can be used for comparison withpower level measurements from other APs.

[0136] Received beacons do not explicitly carry a TP backoff value,however, since beacons are always transmitted at full power theyeffectively carry a TP backoff value of zero. Thus, the AP 12 can updatethe AP KnownAPs table 200 based on a received Beacon. In this case theAP 12 stores the TP backoff value as zero, and sets the normalized powerand the Max Power to the received power level value.

[0137] Additionally, the AP 12 keeps an Age for each entry. The Age isreset to zero, “0”, each time a Beacon or DRCP Announce is received fromthe AP corresponding to the entry. Entries are aged as part of the APPower Adjustment process.

[0138] 2.a.1.2 AP AssociatedSTAs table

[0139] APs 12 also continuously maintain a table of the STAs 16 that areassociated with it—the AP AssociatedSTA table. Referring to FIG. 15, forevery associated STA 16, the AP 12 monitors and collects signal strengthinformation for data packets received (step 220). If an entry for theSTA already exists in the AP AssociatedSTAs table (step 222), that entryis updated (step 224). Otherwise a new entry is created for the STA(step 226). The collected data is periodically analyzed by the AP for APpower adjustment purposes. In addition, whenever a DRCP-active STA 16becomes associated with an AP 12, it sends a Registration Requestmessage to the AP 12. Registration Request messages are sent by the STA16 to the AP 12 periodically until a Registration Acknowledge message isreceived by the STA 16. Upon receipt of a Registration Request from anSTA 16 (step 228), the AP 12 updates the entry in the AssociatedSTATable and marks it as a DRCP-active STA (step 230) and sends aRegistration Acknowledge message to the STA 16 (step 232).

[0140] As shown in FIG. 16, the AP 12's AP AssociatedSTA Table 240maintains the following information about each STA:

[0141] STA-ID—MAC Address of the Station

[0142] Quiet-time—A value representative of the amount of time sincedata was last received from this STA

[0143] DRCP-Active—defaults to false, set to true upon receipt of aRegistration Request

[0144] Distance—Distance (in Banzais, to be further described) to thisSTA, calculated based on signal strength information and TP Backoff

[0145] Max Power—list of power values

[0146] Power samples—number of power samples received

[0147] Normalized_power

[0148] Corrected_power

[0149] sta_load_factor—The load of this STA on this AP, see section 4.c.

[0150] 2.a.1.3 AP Power Adjustment

[0151] During the channel selection process, the AP 12 transmits atmaximum power, that is, it uses a TP backoff value of zero. Once the AP12 has successfully claimed a channel, it calculates a TP Backoff valueand adjust its transmit power for data transmissions down, in accordancewith this value to minimize same channel interference and maximizechannel/bandwidth re-use. The calculation of the TP Backoff value is nowfurther described.

[0152] Generally, with reference to FIG. 17, AP power adjustment isaccomplished as follows: The AP 12 peruses its AP KnownAPs table (step260). The AP 12 finds the AP in the table with the highest TP Backoffvalue. The AP 12 then sets its own Max TP backoff value to the highestTP Backoff value (step 262). This Max TP Backoff value, if used as theAP 12's TP Backoff value, would reduce the AP 12's transmit power to alevel just below the range of the nearest AP operating on the samechannel.

[0153] Once the Max TP backoff is calculated, the AP then scans theAssociatedSTA table to ascertain the distance to the farthest associatedSTA 16 (step 264). The distance to the farthest associated STA 16 iscompared to the distance to the closest AP 12 operating on the samechannel (step 266). If the distance to the farthest associated STA 16 isless than the distance to the closest AP 12, the AP's TP Backoff valueis left at Max TP Backoff (step 268). If the distance to the farthestassociated STA is greater than the distance to the closest AP operatingon the same channel (step 266), then the Max TP backoff value isadjusted back down to accommodate this STA (step 270), and the AP's TPbackoff is set to this adjusted value (step 272). This power adjustmentis periodically repeated to account for changes in the AP KnownAPs tableand the AP AssociatedSTAs tables change (step 274). Power adjustementmay be repeated every second, for example, in an 802.11 environment.

[0154] In accordance with the preferred embodiment for use in a wirelessdata networking environment, as shown in FIG. 18, APs perform the abovedescribed power adjustment as follows. First, the AP 12 checks to see ifits Avoid Other WLANs flag is set (step 280). The AvoidOtherWLANs flagis a configuration parameter which can affect Power Adjustment. In manywireless networking architectures, it is possible for several APs tooccupy the same channel while serving different physical networks. Forexample, in the 802.11 architecture, several APs can serve differentESSs. The AvoidOther WLANs flag is false by default. When set to false,the AP 12 will ignore any other APs on the same channel who's physicalnetwork is different from this AP 12's physical network (e.g. ESS ID).This option is useful for cases when there are multiple APs inrelatively close proximity that are on different networks. In this case,the operator may prefer to run his AP at the maximum power level toprovide the best possible signal for all stations on his network.

[0155] If the Avoid Other WLANs flag is not set, the AP 12 sets its TPBackoff to 0 (step 282). The AP 12 will therefore transmit at fill poweras long as the Avoid Other WLANs flag is not set. If the Avoid OtherWLANs flag is set, the AP proceeds with the power adjustment process andwill not interfere with other APs even if they are operating on adifferent network.

[0156] The AP 12 processes the information in the AP KnownAPs tableevery Hello Interval (step 284), to perform power adjustment. The HelloInterval is architecturally and design dependent. In an 802.11environment, the Hello Interval may be for example the 100 ms beaconinterval. The knownAPs table entries are first aged before otherprocessing is performed. The age of each entry is incremented (step286), and any entries whose age exceeds Max AP Entry Age are deleted(steps 288, 290). Thus, if an AP hasn't been heard from in a while, itis aged out of the table to prevent it from affecting this AP 12's poweradjustment calculations.

[0157] As previously described, the normalized power field of an entry,“n”, of the AP KnownAPs table is determined by averaging over severalreceived power measurement samples. The greater the number of samplesused to derive the value, the more accurate the measurement. The APaccounts for the inaccuracy in this value by subtracting a standarderror, based on the sample size, from the normalized power level, asshown in the following formula. Note, in an 802.11 environment, thenormalized power level is expected be a negative number, ranging invalue from −25 to −90 dBm.

AP knownAPs[n].corrected_power=APknownAPs[n].normalized_power−getStandardError(sample_size);

[0158] In this formula, the function “getStandardError” would return thestandard error for the sample size of “sample_size” in each entry “n”.For example, table I in FIG. 19 shows the standard error values for anumber of sample sizes for RF signal measurements. This formula isapplied to each entry “n” in the AP KnownAPs table to calculate thecorrected_power values for each entry (step 292).

[0159] The AP KnownAPs table is then scanned for the entry correspondingto the AP which was heard at the highest corrected_power level. Thiscorrected_power level is compared to the AP 12's noise floor (step 294).(The AP's noise floor is a measure of background power on the channel.)If the AP 12 finds that the highest corrected_power level is less thanthe AP 12's noise floor, then the AP 12 may transmit at maximum powerwithout interfering with the other APs on the channel. It thereforeleaves its Max TP Backoff value at 0 (step 296). If the AP 12, however,finds that the highest corrected_power level is higher than the AP 12'snoise floor, it needs to set a TP Backoff to avoid interfering with thatAP. In this case the AP 12 calculates Max TP Backoff by subtracting itsnoise floor from the corrected_power associated with that AP (step 298).

[0160] Once it has calculated Max TP Backoff, the AP 12 must thendetermine if there are any associated STAs 16 that are farther away (iewho's signal strength is weaker than) the highest_power_AP. The AP 12'sAssociatedSTAs table is analyzed to find the STA 16 that is the greatestdistance from the AP (step 300). The normalized_power and sample sizevalues for this STA are used to calculate a corrected_power value forthis STA as previously described. The lowest power STA's corrected_powerlevel is compared to the AP 12's noise floor (step 302). If thecorrected_Power level is less than the noise floor, then the AP 12 needsto run at full power to cover the STA, so the AP TP Backoff value is setto 0 (step 304). If the corrected_power level is greater than the AP12's noise floor, then the STA TP Backoff value is set to thecorrected_power level minus the noise floor (step 306).

[0161] Next, Max TP Backoff is compared to STA TP Backoff (step 308).The AP's TP Backoff (“my TP Backoff”) is set to the lower of the twobackoff values to avoid interference with the closest AP while ensuringcoverage for the farthest STA. So, If STA TP Backoff is less than Max TPBackoff, then my TP Backoff is set to the Max TP Backoff value (step310). If STA TP Backoff is greater than Max TP Backoff, then the my TPBackoff value is set to the STA TP Backoff value plus some minimumsignal-to-noise ratio (step 312).

[0162] The AP 12 then adjusts its transmit power by the value of my TPBackoff (step 314), and uses my TP Backoff as the value of TP Backoff inits Announce messages. According to the preferred embodiment, the APwill transmit data at a power level adjusted by TP Backoff, but willtranmsit DRCP management messages (e.g. Claim, Announce, Accept) at fullpower. So, APs can always hear management messages passed between eachother.

[0163] Furthermore, various different wireless networking architecturesmay provide a mechanism for clearing the wireless channel, furtherincreasing the probability that the management messages will bereceived. For example, in the 802.11 architecture, the AP issues a Clearto Send (CTS) message to clear the channel (step 316), and then sends aDRCP Announce message at maximum power (step 318). After sending theAnnounce message at maximum power level, the AP resumes use of itscalculated TP backoff value for data packets to minimize same-channelinterference, as described above.

[0164] 2.a.1.3.i AP Power Adjustment During Station Movement

[0165] When a STA 16 is associated with an AP 12, the AP 12 keeps trackof the distance between the STA 16 and the AP 12. If the AP 12 is usinga non-zero TP Backoff value, and the AP 12 ascertains that the STA 16 ismoving out of range of the AP 12 at backed off power, then the AP 12 canadjust its TP Backoff value to accommodate the STA 16's movement.

[0166] The distance between an AP 12 and an associated STA 16 iscalculated and stored in the AssociatedSTAs table in units of “Banzais”.The Banzai is a unit of distance derived from a measurement of receivedsignal strength from an AP 12 operating with a known transmit powerbackoff. In an 802.11 environment, for example, a received signalstrength measurement is generally expected to range in value from −25dBm to −90 dBm, but depending upon possible antenna gain at the high endor sensitivity at the low end, may range from 0 dBm down to −100 dBm. Atransmit power backoff is generally expected to range in value from 0 dBto 65 dB. Given a received signal strength measurement of“received_power” and transmit power backoff of “TP Backoff” from an AP,the distance to that AP in Banzais is calculated as follows:

distance_in_banzais=ABS[MIN[0, (received_power+tpbackoff)]]

[0167] Algorithms for movement detection are described in more detaillater. For purposes of AP power adjustment, as previously described, theAP 12 collects multiple samples of received_power and TP Backoff valuesfor each STA 16 over time, and the distance between the AP and the STAis calculated over all these samples. The AP 12 detects movement bycontinuously checking to see if the difference between the distance toeach station, derived from a set of long term samples, is sufficientlysmaller that the current distance measurement based on the most recentlycollected samples, to indicate that the STA 16 is moving away from itsAP 12.

[0168] If the AP 12 detects that the STA 16 is moving away and the STA16 is within a given Short Term Standard Error Banzais of the currentedge of the transmit signal (based on the current TP Backoff), then theAP 12 switches to a TP Backoff of 0 until it no longer has any movingSTAs associated with it.

[0169] More particularly, referring to FIG. 20, to detect STA movement,the AP 12 collects a long term samples of distance values for a STA 16(step 320), and then continuously collects short term sample sizedistance values for the STA 16 (step 322). The difference between thelong term distance and short term distance values is compared to aMoving Threshold value plus the standard error in the two distancemeasurements in order to eliminate false movement detection. (Seesection 6 for more information.) A station is considered to be movingwhen the short term distance exceeds the long term distance by more thanthe Moving Threshold plus the sum of the errors in the two measurements.The following pseudo code describes this comparison. IF((AssociatedSTAs[n].short_term_distance − AssociatedSTAs[n].distance) >(movingThreshold + longTermStdError + shortTermStdError)) (step 324)THEN moving = TRUE (step 326) ELSE moving = FALSE; (step 328)

[0170] If the AP 12 detects that the STA 16 is moving, the AP 12 setsits TP Backoff to 0 so that it transmits data at maximum power (step328). The AP 12 remains at maximum power until it detects that the STA16 is no longer moving, or quiet. If the AP 12 determines that it is nolonger moving before the STA 16 loses the association to its AP, the AP12 resumes normal processing of received signal strength to determine anew appropriate TP Backoff value as previously described (step 334).

[0171] Once the AP 12 detects that the STA 16 is moving, it begins usinganother test to detect when the STA 16 has stopped moving. To detectthat the STA 16 has stopped moving, the AP 12 compares the distance tothe STA 16, derived using the Long Term Sample Size, to the distancederived from the most recent Short Term Sample Size samples. The AP 12looks to see when this difference is less than just the standard errorin the two measurements to determine that the STA 16 has stopped moving.This test is performed as follows (step 330): IF((AssociatedSTAs[n].short_term_distance − AssociatedSTAs[myAP].distance)< (longTermStdError + shortTermStdError)) THEN moving = FALSE; (step332)

[0172] 2.b AP Auction

[0173] The purpose of the Auction is to accomplish the distribution ofSTAs 16 across APs 12 in a manner that optimizes wireless communicationsperformance. The goal is to have STAs 16 associate to their nearest AP12 while taking loading (the sum of the individual loads of the STAs 16already associated to the AP 12) into account. This allows the RFfootprints of the APs 12 and STAs 16 to be minimized, while ensuringthat no AP 12 is overloaded.

[0174] STAs 16 learn of available APs 12 through the Announce messagestransmitted by the APs 12. As will be further described with regard toSTA optimization, a STA 16 calculates a “biased distance” to each AP 12it hears from, including its own AP, using the received power andloading information from the Announce messages. A STA 16 will send a Bidmessage to an AP that is “better” than the STA's current AP, wherebetter means that the AP has a lower biased distance. The Bid messagecontains the value of the difference between the biased distance fromthe STA 16 to the destination AP 12 and the biased distance to the STA16's current AP. This value is called the biased distance delta.

[0175] In particular, referring to FIG. 21, the AP 12 collects anyreceived Bids over a period of Auction Interval (steps 340,342). If aBid is received from a STA 16 from which a Bid has already been received(step 344), the new bid information replaces the previous bidinformation (step 346). Otherwise a new entry is created for the STA 16(step 348). In either case the bid entry's age is reset (step 350).

[0176] At the end of Auction Interval (step 352), the AP 12 processesthe received bid information. (The Auction Interval in an exemplary802.11 environment may be on the order of, for example, 7.5 seconds.)The age of all bid entries is incremented by one (step 354) and then anybid entry whose age is greater than Max Bid Age is deleted (step 356).The list is then sorted by biased_distance_delta value (step 358).

[0177] The AP 12 selects the bid entries with the highest biaseddistance delta values, up to acceptsPerAuction entries, and sends a DRCPAccept message to each of the STAs 16 corresponding to those entries(step 360). The IDs of each STA 16 being sent an Accept is put in a listof outstanding accepts (step 362), and a count of accepted STAs who havenot yet associated and registered is noted as numAcceptsOut (step 364).At this point the next auction period begins.

[0178] In addition to receiving DRCP Bids, the AP 12 also receives anindication any time a STA 16 associates to the AP 12. Referring to FIG.22, on receipt of the indication (step 366), the AP checks to see if ithas bid information from the newly associated STA 16 (step 368). Any bidinformation found for the newly associated STA 16 is deleted (step 370).The AP 12 also checks to see if the STA 16 is in the list of outstandingaccepts (step 372), and if the STA 16 is in the accepts outstanding listthat entry is deleted (step 374) and the numAcceptsOut count isdecremented (step 376). At the end of the Auction Interval, anyoutstanding accepts from the previous auction cycle are considered tohave timed out, hence the list of outstanding accepts is emptied andnumAcceptsOut is reset. These processes continue as long as the AP 12 isactive on a given channel.

[0179] 3. STA Initialization:

[0180] The purpose of the STA initialization phase is to find andassociate to a suitable AP 12 to provide the STA 16 with access to thewireless LAN, and to prepare for the operation of the DRCP protocol andalgorithms.

[0181] Referring to FIG. 23, when started, the STA 16 produces a list ofchannels supported by the STA 16 (step 380). In multi-PHY-variant STAs(e.g., STAs supporting multiple bands such as 802.11a/b/g), the channellist will include all of the channels that are supported across thevarious supported bands.

[0182] First, the STA 16 scans for beacons on all channels across allsupported bands (e.g., STAs supporting multiple bands such as802.11a/b/g will scan all channels in each of the a, b, and g bands.)(step 382) The AP 12 that is received at the greatest signal strength isselected (step 384).

[0183] Preferably, where multiple bands are supported, the selection ofan AP 12 also takes into account a preference for the higher bandwidthbands so that, for example as implemented in an 802.11 environment, anAP 12 on an 802.11a or 802.11g channel is given some preference to oneoperating on an 802.11b channel.

[0184] Once an AP 12 is chosen, the STA 16 authenticates and associatesto that AP (step 386). Any security policies that control associationare executed at this point.

[0185] During initialization, the STA 16 also enables the DRCP protocolso that the STA 16 will receive DRCP Announce messages (step 388). TheSTA 16 then proceeds to the STA optimization phase (step 390).

[0186] 4. STA Optimization

[0187] Once it has made its initial association and has access to thewireless LAN, the STA continuously performs the following functions tooptimize its configuration:

[0188] Canvassing. The STA periodically tunes its radio to listen onother channels, while retaining its association to its AP on itsoperating channel. This canvassing of other channels is done to allowthe STA to receive DRCP Announce messages from APs operating on otherchannels.

[0189] Bidding. The STA receives and processes DRCP Announcements fromall APs that are operating within its range on any of its supportedchannels. It evaluates the received power and loading information fromthe Announce messages and if it finds an AP to which it would be moreoptimally associated than its current AP, the STA makes a bid to move tothat AP.

[0190] Radio Power Adjustment. The STA adopts the TP Backoff valuecommunicated in Announce messages from its AP, tracking this value as itchanges.

[0191] Movement Detection. The STA continuously checks to see if it ismoving away from the AP to which it is currently associated. If itdetects that it is moving, it stops participating in the DRCP biddingprocess and adopts a process of next AP selection that is invoked whenthe association to its AP degrades.

[0192] These functions are described more particularly as follows:

[0193] 4.a STA Canvassing

[0194] The process by which the STA 16 canvasses the other channels todetermine whether to send a DRCP Bid message is now described in furtherdetail. In order to monitor DRCP Announce messages, a STA 16periodically tunes its radio to the channels other than the one to whichit is currently associated. However, the STA 16 must remain associatedto its current AP 12 so that it does not lose data packets. So, packetsmust be buffered during the time that the STA 16 is canvassing. Variouswireless communications architectures may provide different means forpacket buffering.

[0195] Generally, referring to FIG. 24, during a periodic scan interval(step 400), the STA 16 causes the AP 12 to which it is currentlyassociated to temporarily buffer the packets destined for the STA 16(step 402). Packet buffering can be initiated in a variety of ways. Forexample, the STA 16 may send a DRCP message to the AP 12 to cause thebuffering, or the AP 12 may periodically turn on buffering and notifythe STA 16 that it has done so. While the STA 16's packets are beingbuffered, the STA 16 tunes its radio to another channel and listens forBeacons and DRCP Announce messages on that channel (step 404). Thisinformation is used by the AP 12 to determine whether to bid for anotherAP. When the scan interval is complete, packet buffering is turned offand the STA 16 receives its buffered packets from the AP 12 (step 406).

[0196]FIG. 25 sets forth a STA canvassing mechanism for use in an 802.11wireless networking environment. The 802.11 architecture convenientlyprovides a power save mode that, in accordance with the principles ofthe invention, can be used for this purpose.

[0197] The 802.11 power save mode is intended for use by STAs 16 so thatthey can turn off their radios for periods of time in order to savepower. STAs 16 can indicate to APs 12 that they are entering this powersave mode. In response, APs 12 buffer the STAs' packets while the STAs16 are “sleeping”. APs 12 periodically send special Beacon messages tothe STAs 16. STAs 16 wake up in response to these special Beaconmessages. These Beacon messages include information as to whether anydata is buffered for the STA 16. The STA 16 “wakes up” if data isbuffered for it.

[0198] STAs 16 operating in an 802.11 environment in accordance with thepreferred embodiment of the invention use the 802.11 power save mode togo off-channel and canvass other channels for DRCP Announce messages.After the channel canvass is complete, the STA 16 reverts to normalpower save mode. Stations that have not been set to Power Save Mode bymanagement are caused by the STA 16 to act as if they've been set to thePower Save Mode. STAs 16 that have already been set to Power Save Modeby management will have even more time to canvass.

[0199] In particular, referring to FIG. 25, at the start of a scaninterval (step 410), the STA 16 inquires about the current state of itspower save mode. The power save mode that was set by management (active,power save) is remembered (step 412). The power save mode is set topower save, and the listen time (time the STA 16 stays asleep), if any,is increased by a period of time herein referred to as scan time (step414). At the beginning of the power save cycle, the STA 16 actuallystays awake temporarily, instead of dozing as it told the AP it wasgoing to do. It is during this time that other channels are canvassedfor beacons and DRCP Announce messages (step 416). After the canvass isdone the STA 16 resumes its power save cycle (step 418). This processrepeats every scan interval. Whenever the STA 16 is not canvassing, itrestores the remembered management set power save mode. The scaninterval may be for example twice per Beacon interval.

[0200] Stations that have not been set to Power Save Mode by managementare caused by the STA 16 to act as if they've been set to Power SaveMode, with listen interval set to the minimum value (i.e., everyBeacon). STAs 16 that have already been set to Power Save Mode bymanagement will have the most amount of time to canvass.

[0201] During the canvass time the STA 16 tunes its radio to a differentchannel in order to passively listen for beacons and DRCP Announcemessages. The STA 16 keeps track of which channels have been canvassed,stepping through all of the channels until all supported channels havebeen canvassed. The STA 16 keeps track of all DRCP Announce messages,and the power level at which they were received.

[0202] 4.a.1 STA KnownAPs Table

[0203] The STA 16 receives beacons and DRCP Announce messages from allAPs 12 within the range of its radio. These are processed to build atable of all known APs 12, the “STA knownAPs” table 430, as shown inFIG. 26. The STA knownAPs table includes the following parameters foreach entry:

[0204] AP-ID

[0205]

[0206] age

[0207] Channel ID

[0208] Load factor

[0209] TP Backoff

[0210] Max Power

[0211] Distance_samples

[0212] Distance

[0213] My_load_factor

[0214] Biased_distance

[0215] The STA Known APs table 430 is built as shown in FIG. 27. Foreach Beacon or Announce message received (steps 432, 434), the STA 16checks to see if it has an entry in the STA KnownAPs table 430 for theAP-ID in the message (step 436). If found, the STA updates the entry(step 438), otherwise it creates a new one (step 340), up to apreviously set maximum herein referred to as Max APs entries (step 442).

[0216] The STA 16 stores the following fields from received beacons inthe STA knownAPs table entries:

[0217] AP-ID

[0218] Channel ID

[0219] Max Power

[0220] The STA 16 stores the following fields from received Announcemessages in the corresponding STA knownAPs table entry:

[0221] AP-ID

[0222] Channel ID

[0223] Received Power

[0224] Load Factor

[0225] TP Backoff

[0226] The STA 16 also notes the received power level that accompaniedthe beacons and Announce messages and uses these values along with theTP backoff values to calculate the distance to the APs in Banzais, aspreviously described. (Again, since non-DRCP APs will always sendbeacons at full-power, the TP Backoff value for these is set to 0.)

[0227] The Received Power and TP Backoff entries are lists, where eachentry in each list corresponds to a Beacon or Announce message receivedfor the corresponding APID. The received power level value andcorrespondingly, the distance in Banzais, are subject to variability inthe RF channel. The STA 16 saves a number of these distance measurementsfor each entry in the knownAPs table, so that it can use averaging to,compensate for this variance, to be further described. For its own AP(i.e. the AP to which the STA is currently associated), the STA 16averages over a relatively large number of distance values, hereinreferred to as “Long Term Sample Size” distance values. For all otherentries, the STA uses fewer, “Bid Sample Size”, distance values.

[0228] Additionally, the STA keeps an Age for each entry. The Age isreset to zero, “0”, each time an Announce message is received from theAP corresponding to the entry. Entries are aged as part of the STABidding process, described below.

[0229] 4.b STA Power Adjustment

[0230] Referring to FIG. 28, an associated and registered STA 16receives all Announce messages from the AP 12 to which it is associated.Upon receipt of an Announce message (step 556), the STA notes the TPBackoff value in the Announce message and adopts that value as the STA'sown TP Backoff (step 558).

[0231] 4.c STA-Bidding

[0232] Each time the STA Canvassing function completes a canvass of allchannels, the STA 16 analyzes the information in the STA knownAPs tableto see if there is a potential “better” AP 12 with which to associate.The notion of what constitutes a better AP takes into account thedistance to the AP in Banzais, the available data rate, and the loading(number of associated STAs) on the AP, if known.

[0233] Referring to FIG. 29, the STA Bidding process operates generallyas follows. When the canvass is complete and a sufficient number ofsamples have been collected on each channel (step 450), the STA knownAPstable 330 entries are aged before other processing is performed (step452). The age of each entry is incremented, and any entries whose ageexceeds Max AP Entry Age are deleted (step 454). Since the age field iscleared each time an Announce message or Beacon is received, this agingprocess will eliminate APs from whom nothing has been heard for “Max APEntry Age” bidding cycles.

[0234] As mentioned, the STA 16 uses averaging to compensate forvariance in its distance measurements. It requires Long Tern Sample Sizedistance values for the STA knownAPs entry corresponding to its AP,before it performs further processing of the table (step 456). Once theSTA 16 has Long Term Sample Size distance values for its own AP, it thenwaits until it has Bid Sample Size distance values for all entries inthe knownAPs list at that time before it begins looking for a better AP(step 458). This is to avoid making a decision to move to a new APbefore it has sufficient information about the other APs in the network.However, to avoid the potential for waiting indefinitely, it will notdelay processing the knownAPs list for any new APs that were added afterit has Long Term Sample Size distance values for its own AP.

[0235] Working with the entries for which there are sufficient distancemeasurement samples, the STA 16 looks for a potential better AP. Insummary, a biased distance is calculated for each entry, which takesinto account the available data rate as well as the loads on the APs(step 460). The data rate is deduced based on the received signalstrength and the technology being used (i.e., in an 802.11 environment,the 802.11 mode of operation (a,b,g)). After calculating the biaseddistances for all of the entries in the STA knownAP table, the AP withthe lowest biased distance is considered to be the best candidate and,if it appears better than its current AP (step 462), a Bid is sent (step464).

[0236] More particularly, referring to FIG. 30, for each entry “n” inthe STA knownAPs table (denoted KnownAPs[n]), the following processingis performed on entry knownAPs[n]. An index of “myAP” corresponds to theentry for the AP to which the STA is currently associated, i.e.,knownAPs[myAP] is the entry for the STA 16's current AP.

[0237] As previously described, the distance field in the STA knownAPstable 430, knownAPs[n].distance per entry, is the distance in Banzais,to the corresponding AP, averaged over a number, Bid Sample Size, ofmeasurement samples. As previously noted, this value is subject tovariance in the RF channel. The bid selection process should preferablyyield the choice of a “better” AP only when the new AP actually wouldprovide better performance for the STA, and not when the new AP simplyappears to be better due to this variance. The variance in the new AP'sdistance measurement is represented by a “Bid Sample Std Error” valuerelated to the bid sample size, and the variance in the current AP'sdistance measurement is represented by a “Long Term Std Error” valuerelated to the long term distance sample size. It is advantageous tominimize the error in the distance measurement for a given entry n, incomparison to the STA's current AP. This is done by using a correcteddistance that is set to the distance to the STA's current AP, if theentry falls within the sum of the standard errors on the two distancemeasurements. The corrected distance, “corrected_distance”, isdetermined as follows: IF ( ABS [knownAPs[n].distance −knownAPs[myAP].distance] ≦ (Bid Sample Std Error + Long Term Std Error)) (step 470) THEN corrected_distance = knownAPs[myAP].distance (step472) ELSE corrected_distance = knownAPs[n].distance; (step 474)

[0238] 4.c.1 Distance to Load Factor Conversion

[0239] The corrected distance to each AP 12 is recorded in the STAknownAPs list. This distance is then used in conjunction with datarelated to the particular wireless environment in which the AP 12 isoperating to derive an estimate on the expected load factor for the STA.For example, in an 802.11 environment, the distance and 802.11 mode(a,b,g) are used to retrieve the expected data rate for the STA 16 fromthe distance_to_rate table: knownAPs[n].data_rate = distance_to_rate[knownAPs[n].mode ] [ knownAPs[n].corrected_distance ] ; (step 376)

[0240] An example of distance to rate calculations for 802.11 modes isshown in Table II in FIG. 31.

[0241] Then, the expected load for this datarate is retrieved from therate_to_load table:

knownAPs[n].my_load_factor=rate_to_load[knownAPs[n].data_rate];  (step478)

[0242] An example of a rate_to_load table for 802.11 networks is shownin Table III in FIG. 32. One skilled in the art will realize how toimplement distance-to-rate and rate-to-load tables from specificationsfor other wireless environments. The corrected_distance andmy_load_factor parameters are determined in this manner for each entry nin the STA Known APs table 430.

[0243] Any entries in the knownAPs list that represent non-DRCP APs needto be given default values for their load_factors so that they can beconsidered by the Stations for associations as well. These defaultload_factors are derived from a default number of STAs per AP value thatshould be consistent across the network and a default “average datarate” per technology. That is: if (knownAPs[n].DRCP_Enabled = = FALSE)then knownAPs[n].load_factor = STAs_per_AP * rate_to_load [ default_rate[ knownAPs[n].mode ] ];

[0244] When determining the load of the STA 16's current AP (myAP), whenmyAP is a non-DRCP AP, then its default load_factor value is preferablyincremented by the STA's load on that AP. This helps to support aconsistent view of the load of that AP both before and after a STAassociates with it—that is, since the STA adds its own load to thedefault load of its prospective (non-DRCP) AP before it makes a decisionto associate with it, it must also add its load to the default load forthis AP after it has associated with it.

[0245] 4.c.2 Biased Distance Calculation

[0246] Using the my_load_factor to the AP 12, the load_factor currentlyon the AP 12 (received from Announce messages) and the correcteddistance to the AP 12, the STA 16 calculates a biased_distance value toaccount for the loading on the prospective AP 12 in comparison to theloading on the STA 16's current AP, as shown in FIG. 29. The biaseddistance is calculated as described by the following formula:knownAPs[n].biased_distance = knownAPs[n].corrected_distance *(knownAPs[n].load_factor+knownAPs[n].my_load_factor)/knownAPs[myAP].load_factor) (step 490)

[0247] Next, a biased distance to the STA 16's current AP 12 iscalculated to account for the loading on the current AP 12 relative tothe loading on the prospective AP. This calculation is made as follows:knownAPs[n].my_ap_rel_biased_distance = knownAPs[myAP].distance *knownAPs[myAP].load_factor/(knownAPs[n].load_factor+knownAPs[n].my_load_factor) (step 492)

[0248] Finally, the difference between the biased distance to theprospective AP and the relative, biased distance to the STA 16's currentAP is determined, as follows: knownAPs[n].biased_distance_delta =knownAPs[n].my_ap_rel_biased_distance − knownAPs[n].biased_distance(step 494)

[0249] After calculating the biased_distances and biased_distance_deltasfor all of the APs in the knownAPs list, the STA 16 checks to see if anyof the biased_distance_delta values are positive (step 496). If not,then the STA 16's current AP is still the best AP, so the STA 16 remainsassociated with its current AP (step 498). Of any positivebiased_distance_delta values, the best AP is the one with the highestpositive biased_distance_delta value (step 500). If the best AP is notDRCP enabled (step 502), then the STA 16 associates with that AP (step504). If the best AP is a DRCP AP (step 502), then a Bid is sent (step506) and the STA 16 resumes normal operation until it either receives aDRCP Accept or it completes another Canvass Sample Number passes of allchannels. If there is more than one AP with the same highestbiased_distance_delta values (step 508), the STA 16 checks to see if anyof them is the last AP to which it Bid (step 510) and if so, it selectsthat one again (step 512).

[0250] If a DRCP Accept is received with the AP-ID matching the selectedAPs AP-ID (step 514), the STA sets its TP backoff value to zero (step516) and associates with the AP from which the Accept was received (step518). The STA 16 now sends a DRCP Registration Request to the AP (step520) and starts a timer (step 522) to go off every Registration TimeoutInterval. When the timer expires (step 524), the STA 16 sends outanother DRCP Registration Request and resets the timer. Upon receipt ofa DRCP Registration Acknowledge (step 526), the timer is disabled (step528).

[0251] If no DRCP Accept is received (step 414) in response to the STA'sBid message after a certain period of time (step 530), the STA remainsassociated with its current AP.

[0252] After the STA 16 has associated with a new AP, the STA 16 waitsuntil it has collected a large number, Long Term Sample Size, ofdistance measurements to its new AP before it resumes this process ofevaluating the knownAPs table for bidding.

[0253] 4.d STA Movement Detection

[0254] When a STA 16 is associated with an AP 12, the STA 16 receivesDRCP Announce messages from all APs 12 within the range of its radio.Referring to FIG. 34, once the STA 16 has collected Long Term SampleSize of distance measurements from Announce messages received from itsAP 12 (step 540), it can begin the movement detection process.

[0255] The STA 16 continuously collects Short Term Sample Size distancevalues to the current AP (step 542). To detect movement, the STA 16compares the distance to its AP 12, derived from averaging over the longterm using Long Term Sample Size, to the short term distance, derivedfrom averaging the most recent Short Term Sample Size samples. Thisdifference is compared to a Moving Threshold value plus the standarderror in these two measurements in order to eliminate false movementdetection. A station is considered to be moving when the short termdistance exceeds the long term distance by more than the MovingThreshold plus the sum of the errors in the two measurements. Thefollowing pseudo code describes this comparison. IF((knownAPs[myAP].short_term_distance − knownAPs[myAP].distance) >(movingThreshold + longTermStdError + shortTermStdError)) (step 544)THEN moving = TRUE (step 546) ELSE moving = FALSE; (step 547)

[0256] Once the STA 16 detects that it is moving (step 446), and as longas the STA 16 does not detect that it has stopped moving, the STA 16refrains from participating in the bidding process (step 548), seeking anew AP only if warranted by the deterioration of its currentassociation. If the STA 16 determines that it is no longer moving beforethe STA 16 loses the association to its AP, the STA 16 resumes normaloperation including participation in the bidding process.

[0257] As in movement detection, to detect that the STA 16 has stoppedmoving, the STA 16 compares the distance to its AP 12, derived using theLong Term Sample Size, to the distance derived from the most recentShort Term Sample Size samples. The STA 16 looks to see when thisdifference is less than just the standard error in the two measurementsto determine that the STA 16 has stopped moving. The following pseudocode describes this test. IF ((knownAPs[myAP].short_term_distance −knownAPs[myAP].distance) < (longTermStdError + shortTermStdError)) (step550) THEN moving = FALSE (step 552)

[0258] If the STA 16 determines that it has stopped moving, the biddingprocess is restarted (step 554).

[0259] 5. Software Architecture

[0260] In accordance with the preferred embodiment, the previouslydescribed functionality is implemented in software in APs 12 and STAs 16respectively. Referring to FIG. 35, the software is implemented inaccordance with a layered architecture, such that it contains a platformdependent module that interacts with a platform independent module. Thisarchitecture is advantageous for porting the inventive functionalitybetween different wireless architecture platforms. As shown each AP 12includes a platform independent module 560 that interacts via an AP API562 with an AP platform dependent module 564. Likewise, each STA 16 (oneshown) includes a STA platform independent module 566 that interacts viaa STA API 568 with a STA platform dependent module 570. In environmentswhere the APs 12 are connected to each other via a wired network 14,DRCP messages may be passed directly between the APs 12 via the wirednetwork 14. In environments where the APs are interconnected via onlythe wireless network 15, APs 12 interact with each other and with STAs16 by passing DRCP messages to the respective platform dependent layer,which causes wireless platform specific protocol messages to be passedbetween the APs 12 and STAs 16 to implement the DRCP protocol.

[0261] Referring to FIG. 36, there is shown a representation of the AParchitecture of FIG. 35 as it applies to in an 802.11 networkingenvironment. The AP Radio Management Agent (ARMA) 580 is the platformindependent layer of the software. The AP Radio Manager (ARM) 582 is theplatform dependent layer of the software. The ARM software is actuallyimplemented within several different 802.11 platform specific elementsof the AP. More information on these elements can be found in theincorporated 802.11 specification.

[0262] Referring to FIG. 37, the Station Radio Manager (SRM) 584 is theplatform dependent portion of the STA software. As shown, the SRMcommunicates with various 802.11 platform specific elements. The StationRadio Management Agent (SRMA) 586 is the platform independent portion ofthe STA software. Likewise, the AP radio manager is the platformdependent portion of the AP software, communicating with 802.11 platformspecific elements. SRMAs communicate with ARMAs through the use of DRCPmessages as previously described.

[0263] These DRCP messages are now described in further detail.Generally, DRCP messages could be encoded as standard LLC data frames,and the invention does not preclude such an implementation. But,according to the preferred embodiment as implemented in an 802.11networking environment, DRCP management messages are encoded as newtypes in existing Class 1 Frames. DRCP messages are addressed either toa Group MAC Address, or to an individual MAC address, and aredistinguished by the presence of the DRCP Protocol Identifier in theProtocol Identification Field of a SNAP PDU.

[0264] The DRCP messages are now described in detail as they operate onan IP WLAN. Some DRCP messages are transmitted as IEEE 802.11 MACmanagement frames of subtype Beacon on the wireless LAN only, whileothers are transmitted as data frames encoded as LLC 1 Unnumbered SNAPPDUs on the wireless LAN or the wired/wireless network between APs.

[0265]FIG. 38 shows the encoding of a DRCP message in an IEEE 802.11Beacon frame. The DA field is set to a specific DRCP group MAC addressas appropriate to the message type, and the BSS ID is a DRCP specificBSS-ID. The fixed portion of the Beacon frame is as defined in the802.11 standard, and the variable portion of the frame is replaced bythe information element created to carry a DRCP protocol message. Inaccordance with a preferred embodiment, it is desirable for DRCP enabledAPs to perform automatic channel selection and load balancing byexchanging DRCP Claim, Preclaim, and Announce messages in managementframes of subtype Beacon, while preventing STAs from attempting toassociate with an AP in response to receipt of one of these messages.Several steps are therefore taken in addition to the DRCP protocolspecific address fields already mentioned. First of all, the “ElementID” field includes an OUI specific to the DRCP protocol, which alertsDRCP enabled APs and STAs that the frame holds a DRCP message.Furthermore, standard (non-DRCP) 802.11 Beacons include in the body ofthe frame field certain fields such as “Supported Rates”, “FH ParameterSet”, “DS Parameter Set”, “CF Parameter Set”, etc. (Refer to theincorporated 802.11 standard document for more information.) Managementframes of type Beacon encoding 802.11 Claim, Preclaim, and Announcemessages either do not include these fields, or set them to a nullvalue. Non-DRCP STAs that might otherwise attempt to use the DRCP Beacontype frames for association cannot do so due to the lack of thisinformation.

[0266]FIG. 39 shows the encoding of a DRCP message within an 802.11 MACData frame, of subtype Data. DRCP messages are addressed either to anindividual MAC address or to one of the DRCP Group MAC addresses, andare distinguished by the presence of the DRCP Protocol Identifier in theProtocol Identification Field of a SNAP PDU. DRCP messages that aretransmitted over the DS may be formatted as shown, or may be similarlyencoded in another MAC data frame depending upon the DS media.

[0267] In accordance with the preferred embodiment, the SRMAs and ARMAsinteract with the SRMs and ARMs to generate and/or collect informationneeded to produce or interpret DRCP protocol messages. It is noted thatthe DRCP protocol could be implemented over non-802-11 primitiveswithout departing from the principles of the invention. The followingdescribes the primitives used in an 802.11 environment.

[0268] 5.a Enhancements to Standard 802.11 MAC Service Interface

[0269] The ARMAs and SRMAs transmit and receive DRCP messages over astandard 802 MAC Service Interface, with some enhancement. The receiveinterface is enhanced in both the STA and the AP to allow the SRM andthe ARM to indicate to the SRMA and ARMA respectively, the power atwhich DRCP messages are received. In particular, the semantics of the802.11 MA-UNITDATA.indication service primitive are modified as shown bythe underlined text, to add a received power parameter as follows:MA-UNITDATA.indication ( source address, destination address, routinginformation, data, reception status, priority, service class, receivedpower )

[0270] The received power parameter specifies the signal strength,expressed in dBm, at which the MSDU was received. The received powervalue indicates the current level at which the sending device is heard,but does not provide an indication of whether or not the sending deviceis transmitting at full power. The potential power level at which adevice might be heard can be determined when the transmit power backoff(i.e., the amount, in dB, by which the radio is turned down) in use bythe device is also known.

[0271] 5.b Enhancements to the Standard 802.11 Management Interface

[0272] BSS Description

[0273] The BSSDescription Parameter contains a list of elements thatdescribe the BSS. An additional element is added to this list: Name TypeValid Range Description Received Integer −1 to −99 Indicates the power(in dBm) Power at which the Beacon from this BSS was received.

[0274] Send DRCP

[0275] This mechanism is provided to allow the ARMA to send DRCPMessages encoded in 802.11 Management frames of type Beacon.

[0276] MLME-SENDDRCP.request

[0277] This primitive is used by the ARMA to request that the ARM send aDRCP Message over the wireless media, encoded in an 802.11 Managementframe of type Beacon. As shown in FIG. 34, this is a special type ofBeacon frame wherein the fixed portion of the Beacon frame is as definedas in the 802.11 standard, and the variable portion of the frame isreplaced by a single information element that carries the DRCP message.

[0278] The primitive parameters are as follows: MLME-SENDDRCP.request (Destination Address Message Length DRCP Message Quiet Channel CTSDuration ) Name Type Valid Range Description Destination MAC N/A Aspecific DRCP group MAC Address Address address as appropriate to themessage type. Message Unsigned  0 . . . 2312 Indicates the number ofoctets Length Integer in the DRCP Message field. DRCP DRCP N/A DRCPMessage Message Message Quiet Boolean FALSE (0), Indicates whether theSTAs Channel TRUE (1) associated to the AP should be quieted for theBeacon transfer by the transmission of a Clear To Send (CTS) frameimmediately prior to the Beacon transfer. CTS unsigned 16 . . . 255Indicates the value to be Duration integer _sec placed in the durationfield of the CTS frame. The value represents the time, in microseconds,required to transmit the pending Beacon frame, plus one short interframespace (SIFS) interval. This parameter is only used when the quietchannel parameter is true.

[0279] This primitive is generated by an ARMA to request that a DRCPMessage be sent on the wireless media encoded in an 802.11 Managementframe of type Beacon. DRCP Claim and Hello messages are sent in thismanner. As previously described, the ARMA may optionally quiet thechannel before sending a DRCP Hello message by first by sending a CTSframe. In particular, if the Quiet Channel parameter is TRUE, the ARMtransmits a Clear To Send (CTS) frame immediately prior to the Beacontransfer. The DRCP Hello CTS Destination MAC Address is placed in theReceiver Address (RA) of the CTS frame. The duration field of the CTS isset to the value of the CTS Duration parameter.

[0280] The fixed portion of the Beacon frame is as defined in the 802.11standard. The DA is set to the Destination Address parameter value, theSA is the AP's MAC address, and the BSS ID is the DRCP Default BSS-ID..The variable portion of the frame is replaced by a single informationelement with an Element ID of DRCP Protocol, with a Length field valueof the Message Length parameter and the Information field containing theDRCP Message.

[0281] MLME-SENDDRCP.confirm

[0282] This primitive confirms the transmission of a DRCP message to theARMA. The primitive parameters are as follows: MLME-SENDDRCP.confirm (ResultCode ) Name Type Valid Range Description ResultCode EnumerationSUCCESS, Indicates the INVALID_PARAMETERS, result of the NOT_SUPPORTEDMLME-SENDDRCP.request

[0283] This primitive is generated by the MLME as a result of anMLME-SENDDRCP.request to send a DRCP message encoded in an 802.11Management frame of type Beacon. The ARMA is thus notified of the resultof the Send DRCP request.

[0284] Power Management Fib

[0285] As previously described, one way that a STA can support periodiccanvassing is to indicate to the AP that it is in power save mode,thereby causing the AP to buffer the STAs packets while the STA iscanvassing. This mechanism supports a STA's ability to indicate to theAP that it is in power save mode, without actually going into power savemode.

[0286] MLME-POWERMGTFIB.request

[0287] This primitive requests the SME to use the power save modeinteraction with the AP to allow time to canvass other channels. Theprimitive parameters are as follows: MLME-POWERMGTFIB.request ( ) NameType Valid Range Description Null N/A N/A No parameters

[0288] This primitive is generated by an SRMA to cause the MLME toborrow part of the doze time (if the STA is in power save mode) or allof the doze time (if the STA is in active mode) in order to canvassother channels.

[0289] This request causes the SRM to:

[0290] 1. save the current power management mode settings

[0291] 2. set:

[0292] a. power management=Power_Save

[0293] b. WakeUp=FALSE

[0294] c. ReceiveDTIMs=FALSE

[0295] 3. signal the AP that it is using power management mode.

[0296] This request prepares the SRM to:

[0297] 1. at the start of the power save cycle, signal the SRMA bysending an MLME-PSSTART.indication while actually keeping the power on.

[0298] 2. catch any user or net manager power mode management operationsand cause them to use the saved settings, not the active settings.

[0299] MLME-POWERMGTFIB.confirm

[0300] This primitive confirms the change in power management mode tothe SRMA. The primitive parameters are as follows:MLME-POWERMGTFIB.confirm ( ResultCode ) Name Type Valid RangeDescription ResultCode Enumeration SUCCESS, Indicates theINVALID_PARAMETERS, result of the NOT_SUPPORTED MLME-POWERMGMTFIB.req

[0301] This primitive is generated by the MLME as a result of anMLME-POWERMGTFIB.request to mimic power save mode. The SRMA is thusnotified of the change of power mode indicated.

[0302] Power Save Start

[0303] This mechanism notifies the SRMA that it can begin to canvass.

[0304] MLME-PSSTART.indication

[0305] This primitive indicates to the SRMA the start of the power savecycle. The STA does not actually power off its radio and enter the sleepstate at this point, but preferably, it should not transmit outgoingframes after sending this indication until it receives anMLME-PWRMGMTFIBCONTINUE.request. The primitive parameters are asfollows: MLME-PSSTART.indication ( ) Name Type Valid Range DescriptionNull N/A N/A No parameters

[0306] This primitive is generated by an SME to indicate the start ofpower save cycle. The SRMA is thereby notified of the start of the powersave cycle.

[0307] Power Management Restore

[0308] This mechanism further supports a STA's ability to indicate tothe AP that it is in power save mode, without actually going into powersave mode.

[0309] MLME-PWRMGMTRESTORE.request

[0310] This primitive tells the MLME that it should restore theuser-configured power save mode. This primitive allows the SRMA to tellthe MLME that it no longer needs to lie to the AP about power save (thatcontrol over power save is passed back to the MLME). The primitiveparameters are as follows: MLME-PWRMGMTRESTORE.request ( ) Name TypeValid Range Description Null N/A N/A No parameters

[0311] This primitive is generated when the canvass mechanism is takenout of service. The receipt of this primitive causes the SRM to restorethe saved power management mode settings and:

[0312] 1. if saved power mode was ACTIVE, immediately force the awakestate;

[0313] 2. if saved power mode was POWER_SAVE, continue normal power savemode operation.

[0314] MLME-PWRMGMTRESTORE.confirm

[0315] This primitive confirms the change in power management mode tothe SRMA. The primitive parameters are as follows:MLME-PWRMGMTRESTORE.confirm ( ResultCode ) Name Type Valid RangeDescription ResultCode Enumeration SUCCESS, Indicates the result of theINVALID_PARAMETERS, MLME.PWRMGMTRESTORE.req NOT_SUPPORTED

[0316] This primitive is generated by the MLME to confirm that the SMEhas executed an MLME-PWRMGMTRESTORE.request. It is not generated untilthe change has been indicated. Upon receipt of this primitive, the SRMAis notified of the change of power mode indicated.

[0317] Power Management Fib Continue

[0318] Once canvassing is complete, this mechanism informs the SRMA thatit “has control” of the radio and communicates power save state (awakeor doze).

[0319] MLME-PWRMGMTFIBCONTINUE.request

[0320] This primitive tells the MLME that it's safe to enter the awakestate and transmit frames if desired. The primitive parameters are asfollows: MLME-PWRMGMTFIBCONTINUE.request ( ) Name Type Valid RangeDescription Null N/A N/A No parameters

[0321] This primitive is generated when the SRMA is has completedcanvassing. Upon receipt, the MLME enables transmission of user dataframes, if necessary.

[0322] MLME-PWRMGMTFIBCONTINUE.confirm

[0323] This primitive confirms the change in allowed power managementstate. The primitive parameters are as follows:MLME-PWRMGMTFIBCONTINUE.confirm ( ResultCode ) Name Type Valid RangeDescription ResultCode Enumeration SUCCESS, Indicates the result of theINVALID_PARAMETERS, MLME.PWRMGMTFIBCONTINUE.req NOT_SUPPORTED

[0324] This primitive is generated by the MLME to confirm that the SMEhas executed an MLME-PWRMGMTFIBCONTINUE.request. It is not generateduntil the change has been indicated. Receipt by the SRMA serves asnotification of the change of the allowed power save mode.

[0325] Channel Out

[0326] This mechanism supports the ability to indicate to an ARMA that achannel has gone out of service.

[0327] MLME-CHANNELOUT.indication

[0328] This primitive reports to the ARMA that a channel that waspreviously available has become unavailable. The primitive parametersare as follows: MLME-CHANNELOUT.indication ( Channel ) Name Type ValidRange Description Channel Integer 0-255 Channel identifier

[0329] This primitive is generated by the MLME when a channel becomesunavailable. Receipt of this primitive causes the ARMA to remove thechannel from its channel map.

[0330] Channel In

[0331] This mechanism provides the ability to indicate to an ARMA that achannel has gone into service.

[0332] MLME-CHANNELIN.indication

[0333] This primitive reports to the ARMA that a channel that waspreviously unavailable has become available. The primitive parametersare as follows: MLME-CHANNELIN.indication ( Channel ) Name Type ValidRange Description Channel Integer 0-255 Channel identifier

[0334] This primitive is generated by the MLME when a channel becomesavailable. Receipt of this primitive causes the ARMA to add the channelto its channel map.

[0335] Beacon Notify

[0336] This mechanism supports the ability to detect any other APs usingthe same channel.

[0337] MLME-BEACONNOTIFY request

[0338] This primitive requests the MLME to notify the ARMA whenever abeacon is received. There is one indication for each Beacon received. Anindication is generated any time a Beacon is received on the currentchannel. The primitive parameters are as follows:MLME-BEACONNOTIFY.request ( Notify Enable ) Name Type Valid RangeDescription Notify Boolean True or False When True, indicates that theEnable PIOTE is to be notified of any Beacons received. When False, thismechanism is to be disabled.

[0339] This primitive is generated by an ARMA when it wants to benotified of any beacons received on its own channel. Receipt of thisprimitive by an MLME causes the MLME to enable a mode whereby the ARMAwill be notified if any Beacon is received.

[0340] MLME-BEACONNOTIFY confirm

[0341] This primitive confirms the change in the beacon notificationmechanism. The primitive parameters are as follows:MLME-BEACONNOTIFY.confirm ( ResultCode ) Name Type Valid RangeDescription ResultCode Enumeration SUCCESS, Indicates the result of theINVALID_PARAMETERS, MLME-BEACONNOTIFY.requ NOT_SUPPORTED

[0342] This primitive is generated by the MLME as a result of anMLME-BEACONNOTIFY.request. Reciept of this primitive by the ARMA servesas notification of the change of Beacon Notify as indicated.

[0343] MLME-BEACONNOTIFY indication

[0344] This primitive reports to the ARMA that a Beacon was received onthe data channel. The primitive parameters are as follows:MLME-BEACONNOTIFY.indication ( BSSDescription ) Valid Name Type RangeDescription BSSDescription BSSDescription N/A The BSS Description(including any additional Description Elements defined in 0) pertainingto an individual Beacon that was received.

[0345] This primitive is generated by the MLME if a beacon is receivedon the data channel. Note that a separate MLME-BEACONNOTIFY.indicationis generated for each beacon received, so the primitive parameter willonly ever contain a single BSSDescription. Upon receipt of thisprimitive, The ARMA is notified of the Beacon and the signal strength atwhich it was received.

[0346] 5.c DRCP Messages Preferred Implementation

[0347] The following describes the manner in which the above describedprimitives are used to implement DRCP messages in an 802.11 environment.FIG. 40 shows a summary of the DRCP messages that are used to implementthe previously described functionality. FIG. 41 shows field definitionsused in DRCP messages, as follows:

[0348] DRCP Preclaim

[0349]FIG. 42 shows the format of the DRCP Preclaim message. A DRCPPreclaim message is encoded in an 802.11 Management frame of typeBeacon. The ARMA sends a DRCP Preclaim message using theMLME-SENDDRCP.request management primitive with the followingparameters:

[0350] Destination Address—DRCP All ARMAs Group MAC Address

[0351] Message Length—12

[0352] DRCP Message—Preclaim Message

[0353] Quiet Channel—FALSE (0)

[0354] CTS Duration—0

[0355] DRCP Claim

[0356]FIG. 43 shows the format of the DRCP Claim message. A DRCP Claimmessage is encoded in an 802.11 Management frame of type Beacon. TheARMA sends a DRCP Claim message using the MLME-SENDDRCP.requestmanagement primitive with the following parameters:

[0357] Destination Address—DRCP All ARMAs Group MAC Address

[0358] Message Length—16

[0359] DRCP Message—Claim Message

[0360] Quiet Channel—FALSE (0)

[0361] CTS Duration—0

[0362] DRCP Announce

[0363]FIG. 44 shows the format of the DRCP Announce message. A DRCPAnnounce message is encoded in an 802.11 Management frame of typeBeacon. The ARMA sends a DRCP Announce message using theMLME-SENDDRCP.request management primitive with the followingparameters:

[0364] Destination Address—DRCP All Agents Group MAC Address

[0365] Message Length—16

[0366] DRCP Message—Announce Message

[0367] Quiet Channel—FALSE (0)

[0368] CTS Duration—0

[0369] DRCP Bid

[0370]FIG. 45 shows the format of the DRCP Bid message. A DRCP Bidmessage is encoded as an LLC 1 Unnumbered SNAP PDU in a data frame. Themessage is addressed to the Individual MAC Address of the AP in whichthe target ARMA is instantiated. The SRMA sends a DRCP Bid message overthe standard MAC Service Interface.

[0371] DRCP Accept

[0372]FIG. 46 shows the format of the DRCP Accept message. A DRCP Acceptmessage is encoded as an LLC 1 Unnumbered SNAP PDU in a data frame. Themessage is addressed to the Individual MAC Address of the STA in whichthe target SRMA is instantiated. The ARMA sends a DRCP Accept messageover the standard MAC Service Interface for relay to the DS.

[0373] DRCP Registration Request

[0374]FIG. 47 shows the format of the DRCP Registration Request message.A DRCP Registration Request message is encoded as an LLC 1 UnnumberedSNAP PDU in a data frame. The message is addressed to the Individual MACAddress of the AP in which the target ARMA is instantiated. The SRMAsends a DRCP Registration Request message over the standard MAC ServiceInterface for relay to the DS.

[0375] DRCP Registration Acknowledge

[0376]FIG. 48 shows the format of the DRCP Registration Acknowledgemessage. A DRCP Registration Acknowledge message is encoded as an LLC 1Unnumbered SNAP PDU in a data frame. The message is addressed to theIndividual MAC Address of the AP in which the target SRMA isinstantiated. The ARMA sends a DRCP Registration Request message overthe standard MAC Service Interface for relay to the DS.

[0377]6. Movement detection

[0378] As previously described, APs and STAs ascertain movement basedupon evaluation of short and long term averages of parameters, alongwith expected error measurements. In accordance with an aspect of theinvention, movement detection is achieved through application of abroader inventive concept that provides a way to ascertain the dynamicattributes of a system based upon short and long term averages ofdiscrete data measurements. The principles of this invention apply toany system in which a discretely measured variable may change widely.For purposes of clarity, however, the invention is now described interms of its particular application to wireless networks.

[0379] In a wireless network such as the one shown in FIG. 1, a wirelessnetworking user (heretofore also referred to as “STA”) is associatedwith an access point (AP). The AP provides associated users with networkconnectivity via radio frequency (RF) signals. Various APs are used toprovide seamless RF coverage, so that when the user moves away from oneAP toward another AP, the user will associate with the closer AP (or theAP that is more lightly loaded) and seamless network functionally isthereby maintained. It is therefore important to be able to ascertainthe location of a user relative to an AP so that a determination can bemade as to whether the user is currently moving. This allows the systemto assure that the user rapidly becomes associated with the closest APso the overall system performance is maximized. As a user moves towardor away from an AP, the received power level (i.e. the power of the RFsignal received by the user from the AP) goes up or down respectively.Thus, one way to ascertain user movement is by monitoring received powerlevels.

[0380] However, received power levels can appear to vary greatly evenwhen a user is not moving. For example, the opening or closing of adoorway can cause either a gain or attenuation in the user's receivedpower level. A person waving their hand near the user's antenna can evencause a gain or attenuation in received power level. Environmentalinterference can also cause changes in received power levels. Thesevarious changes in power level can cause a user to appear to be movingwhen in fact he or she is not. This can cause the user to roamneedlessly between APs, particularly in environments where APs are closetogether and their transmit power levels are lower than maximum power.Alternatively, variations in signal power due to these effects can maskthe fact that the user is indeed moving. In this case, the system couldfail to detect the motion and fail to associate the user with theappropriate AP. FIG. 49 shows an example graph of discrete measurementsof received power vs. time for a user who is not moving. As can be seen,the inaccuracies in data sampling prevent any assumption of movement inone direction or the other.

[0381] As a more particular example, consider an 802.11 a wirelessnetwork. APs in such a network provide a maximum bandwidth of 54 Mbps.Bandwidth drops with distance from the AP. Assume that adjacent APs havetheir transmit power adjusted so that each provides a 54 Mbps cell onthe order of about 10 feet in diameter. A walking user might be able totransition through such a cell in 2 seconds. On the other hand, a usersitting at his desk (near the center of the cell, right next to the AP)who gets up and leaves travels only 5 ft, not 10 ft to the edge of thecell—so, it may take the user only just over a second to be in the aisleand out of the cell. These examples provide a motivation for why rapidpower estimates based on discrete measurements must be made. Increasingsampling rates increases accuracy, but this also causes more overhead interms of wireless channel bandwidth, interrupt activity and processingoverhead on the user device. Some user devices could be simpleappliances such as phones, digital assistants, etc. and have verylimited processing power. So a trade-off must be made between samplerate and overhead.

[0382] According to one possible implementation, power levels aremeasured at intervals over a window of time and a roaming decision ismade. In an 802.11a network, when a user is about 1ft from an AP whosepower is set so that it has a 54 Mbps cell which is about 10 ft indiameter, the user's true mean power level should be about −38 dbm.Assume a 99% confidence interval around the true mean (i.e. the powerlevel to be estimated) is desired. Yet, there is a variability to themeasurements because of environmental effects (hand waving, etc.) aswell as inherent inaccuracy in the implementation measurement itself.Assume these inaccuracies and statistical variability in the data resultin distribution of the data with a standard deviation, σ=15 dbm.Referring to FIG. 50, if only 8 samples are taken in such a statisticaldistribution, then the 99% confidence interval around this (true) meanis −23.4 dbm to −52.6 dbm.

[0383] The 99% confidence interval has a range of |52.6−23.4|=29.2 dbm,or about 30 dbm. This is about ±15 dbm. So, because of the variabilityin the signal, if only 8 samples are taken, all that can be known isthat the “true power” lies somewhere between −23.4 dbm and 52.6 dbm andthat such conclusion can be drawn with 99% assurance.

[0384] If less accuracy can be tolerated, for example 95% or even 90%confidence, the resultant range would be narrower. But, lower confidenceintervals increase the likelihood of “false positives”. A false positiveoccurs when a user is ascertained to be moving when in fact he or she isnot, causing the user to needlessly roam to another AP. It is desirableto minimize such false positives as they needlessly consume valuablebandwidth.

[0385] When a user doubles his or her distance from an AP, the user'sreceived power decreases by 6 db. So, when a user moves from 1 foot awayto 2 feet to 4 feet away from the AP (almost to the edge of the cell),the (true) average received power has decreased from−38 dbm to −44 dbmto −50 dbm respectively. But, as seen in FIG. 51, when trying toestimate the average received power from eight samples taken during thismotion with a 99% confidence interval in the data, it cannot beascertained that the user has moved. This is because the true mean isreally unknown. All that is known is that it lies somewhere between−23.4 dbm and −52.6 dbm. So, when only these few samples are taken, itcannot be ascertained whether the user is moving away from the AP,getting closer to the AP, or not moving at all.

[0386] Of course increasing the number of samples taken decreases therange of error. If 20 power samples are taken, then the 99% confidenceinterval is −29.1 dbm to −46.9 dbm. But, taking lots and lots of sampleswill take too long unless channel overhead is increased.

[0387] Now consider taking n samples to produce an estimate, and thentaking n more to produce a second estimate. The two estimates are thencompared to see if a conclusion can be drawn as to whether the user ismoving. If the confidence intervals around each estimator are large,e.g. 99%, then there exists a spectrum of outcomes and again it cannotbe ascertained as to whether the user is moving toward or away from theAP, or not moving at all. In FIG. 51, to tell that the user is movingaway from the AP with 99% assurance, the upper edge of the rightconfidence interval must be positioned below the lower edge of the leftconfidence interval.

[0388] Consider two basic scenarios regarding motion in wirelessnetworks:

[0389] (1) The user stays in one place for a reasonable time and thenmoves to a new place. The user requires communication while moving, but,the user tends to move and then stop and stay somewhere for a while. Orsimilarly, the user may move very slowly within one confined area, andthen move more rapidly to another area.

[0390] (2) The user is constantly in motion.

[0391] In the instance of scenario #1, which describes the very largemajority of user activity in wireless networks, the accuracy of thepower estimate can be greatly improved. In accordance with theprinciples of the invention, two averages of the received signalstrength are maintained as above. But, one is the most recent N₁ samplestaken over a sliding window, and the other is a long term average, usingN₂ samples. So both a long term average and a short term average aremaintained. Referring to FIG. 52, the confidence interval around thelong term average is very small. The error in the estimate is almostcompletely removed. Therefore, the potential uncertain outcomes in thedecision are reduced.

[0392] In FIG. 53, when the user is moving away from the AP, the upperedge of the right confidence interval will fall below the long termaverage (which has essentially a confidence interval of close to ±0 db.)

[0393] For a given application, one needs to ascertain how many samples(N₂) must be taken such that the long term average estimate hasessentially 0 error. Also, it is desirable to ascertain how few samples(N₁) are needed in the short term average to be able to make a decisionwith 99% accuracy.

[0394] Assume a user starts at a position 1 foot away from the AP andmoves towards the edge of the 10 ft cell. The goal is to find out howfew samples are required to ascertain that the user is moving with 99%accuracy, in order to produce the most robust implementation from anoverall performance perspective. If it were possible to “perfectly”measure power, a −6 db drop would be observed each time the user doubleshis distance from the AP. Referring to FIG. 54, if the power level is−38 dbm when the user is at 1 foot, it is −44 dbm at 2 feet and −50 dbmat 4 feet which is almost at the edge of the cell. As can be seen in theFigure, when the short term average is −50 dbm and the upper edge of the99% confidence interval is just below −38 dbm, then the confidenceinterval has a width of ±12 db. To achieve such a confidence interval,14 samples (N₁) are required in the short term, given the previouslyassumed standard deviation of the data, σ=15 db. With these 14 samples,the 99% confidence interval is −60.7 dbm<−50<−39.2 dbm.

[0395] In this wireless network example, it has been assumed that a usercan walk from the center of the cell to the edge of the cell in 1.5seconds. So, samples need be taken every 1.5÷14≈100 milliseconds. As afurther improvement, it would be desirable to use 16 samples so thatdivision can be done by a processor via a shift operation. Thisincreases computational efficiency on the user's machine. This increasesthe sample rate a negligible amount.

[0396] Regarding the long term average, it may be reasonable to toleratea ±1 db confidence interval around the long term estimate. The tighterthis interval needs to be, the longer the user has to stay near the AP,or stay relatively stationary within a certain area, to cause theaverage to converge. It is desirable to calculate how little time theuser needs to stay in place to achieve an accuracy of ±1 db with 99%confidence. Assume, reasonably, that signal strength samples are takenbased on messages received from the AP every 50 milliseconds. Referringto the table shown in FIG. 54, it is seen that if the user stays nearthe AP (1 ft) for about 1.5 minutes, and samples occur every 50milliseconds, the accuracy of the power estimate becomes less than ±1db.

[0397] The preferred implementation for the current wireless networkexample thus utilizes: (a) a short term average over N₁=16 samples, (b)a long term average over 2048 samples, and (c) “N₂” which is the numberof samples taken so far in computing the long term average. The processis as follows:

[0398] (1) continually calculate the long term average. The long termaverage is not “stable” until at least 2000 samples have been taken.This takes 1.5 minutes at 50 milliseconds per sample. An implementationpreferably accumulates 2048 samples to make the division a shiftoperation.

[0399] (2) calculate a short term average with the most recent N₁=16samples. (16 is used instead of 14 so that the division is accomplishedvia a shift.)

[0400] (3) When the difference between the short term and long termaverages is greater than 12 db then it is known with 99% accuracy thatthe user is moving.

[0401] (4) When the user roams to a new AP, the counter used tocalculate the long term average samples is reset to 0. Then the longterm average is not stable again for another 2048 samples.

[0402] In an environment where users tend to remain in a cell for lessthan 1 second, the long term estimate could be used based on fewersamples. However, this will result in an increased risk of falsepositives. Several alternatives can be considered to mitigate theoccurrence of false positives:

[0403] (1) if the user has just arrived in a new cell (i.e. N₂≦32) thenrequire at least 32 samples before allowing a power-based roamingdecision. This puts some hysteresis into the system. There will be somefalse positives though. If the user roams to a new AP and then back tothe old one, false positives may be occurring. It may then help torequire that N₂≦64 for example. This helps the confidence intervalmaking it −42.8 dbm<−38<−33.1 dbm.

[0404] (2) Take into account the signaling rate. For example, the longterm average accumulates while the number of samples (N₂) grows. But, ifthe user's data rate has dropped, then the user has moved outside the 54Mbps inner circle by definition. Roaming should be initiated at thispoint.

[0405] (3) Once a user has roamed to a new cell, the user should become“sticky” and try to stay there until the user is near the edge of thecell. Here it may be useful to require that N₂≧128, for example, plussee the data rate drop.

[0406] To generalize, in a system wherein particular dynamic attributesare to be ascertained (e.g. “is the wireless network user in motion”),short term and long term averages of a system variable (e.g. signalstrength) are calculated. An acceptable difference between the short andlong term averages is calculated which positively identifies the systemcharacteristic (e.g. the user has moved.)

[0407] Referring to FIG. 55, the steps are generally as follows:

[0408] 1. Define a system dynamic attribute to be ascertained (step600). For example, in the wireless network example, the dynamicattribute to be ascertained is whether a user is moving. In the networkusage example, the dynamic attribute to be ascertained is whetherbandwidth for a user should be increased.

[0409] 2. Define a system variable to be monitored to ascertain thedynamic attribute (step 602). For example, in the wireless networkexample, the variable is received signal strength. In the network usageexample, the variable could be number of packets injected onto thenetwork by the user.

[0410] 3. Ascertain the statistical characteristics of the systemvariable measurements (step 604). This will include specification andanalysis of individual system and environmental factors that contributeto statistical variations in the system variable(s). In the wirelessnetwork example, the standard deviation of the signal strengthmeasurement is affected by environmental noise, implementationimprecision, spatial events and motion. In the network usage example thestandard deviation is affected by the degree of burstiness in thetraffic generated by the user, the speed of the user's computer,contention and interleaving effects with other network traffic, andhigher layer network protocol parameters.

[0411] 4. Choose the range of the true mean for the system variable thatwould indicate that the dynamic system attribute has been identified(step 606). For example, in the wireless network example, when the truemean of the signal strength has changed by 12 db, the systemattribute—the user has moved—has been positively identified. In thenetwork usage example, one may decide that when the true mean for numberof packets injected into the network by a user has exceeded a threshold,the user's bandwidth should be increased.

[0412] 5. Pick a confidence interval based on the accuracy of decisionsto be made regarding the dynamic system attribute (step 608). The rateof “false positive” decisions and “false negative” decisions iscontrolled by how accurately the dynamic system attribute is estimated.Calculating that attribute with a higher confidence interval improvesthat accuracy. In the wireless network example, the confidence intervalwas 99%.

[0413] 6. Calculate the number of samples of the variable that must betaken such that the confidence interval around a given metric (such asthe average) results in a spread that is minimized to a pre-determinedamount based on the decision accuracy desired (step 610). In thewireless network example, this was +/−1 db.

[0414] 7. Set a long term average based on at least the number ofsamples obtained in step 6 (step 612). (This average is cumulative asopposed to a moving window.)

[0415] 8. Given the range chosen in step 4, calculate the number ofsamples of the variable that must be taken such that the confidenceinterval around a given metric (such as the average) results in a spreadthat is less than the range (step 613). This calculation depends uponthe standard deviation in a known manner. This calculation is well knownin the field of statistics as “sample size estimation”. Statisticalstudies which use a subset (N) of members of a population need to bedesigned so that inferences taken from the sample set are statisticallysignificant and representative of the entire population. Specificknowledge, or implicit assumptions, regarding the statisticalcharacteristics of the dynamic system variables obtained in Step 3 areused to compute the sample set size. For more information on knownstatistical methods for sample size computation, reference is made to“Statistical Analysis”, Sam Kash Kachigan, Radius Press, NY 1986 (ISBN:0-942154-99-1), and in particular to Section 8-11, pg 157, “ParameterEstimation, Sample Size Selection for Limiting Error”, and Section 9-10,pg 189, “Sample Size Selection for Desired Power”

[0416] 9. Set a short term average moving window based on the number ofsamples obtained in step 8 (step 614).

[0417] 10. Calculate the absolute difference between the long termaverage and the short term average (step 516). If the difference isgreater than the range chosen in step 4, then the dynamic systemattribute has been positively identified (step 618). In the wirelessnetwork example, when the difference exceeded the range, it was knownwith 99% confidence that the user was moving or had moved. In thenetwork usage example, if the difference between short term averagepacket count and long term average packet count exceeds the chosenrange, this indicates that the user should be granted higher bandwidth.If the difference between the long term average and the short termaverage is greater than the range chosen in step 4, then the dynamicsystem attribute has not been positively identified (step 620), and N1moving window samples continue to be collected.

[0418] In FIG. 56 there is shown a block diagram showing a wirelessnetworking system that implements the invention. A user (STA 16)communicates with an AP 12 over the wireless network. The user sendsmessages to the AP that indicate the received signal strength from theAP as perceived by the user. These messages are collected by the AP(640). A processor 642 in the AP uses the messages to compute the shortand long term averages according to the process as described in FIG. 55.When it is ascertained that the user has moved, an indication 644 isset.

[0419] In FIG. 57 there is shown a block diagram of a preferredembodiment of a wireless networking system that implements theinvention. A user device (STA 16) communicates with an AP over thewireless network. The user message collection mechanism 646 receivesmessages from the AP and monitors the received signal strength of themessages. A processor or hardware state machine 648 in the user deviceuses the signal strength of the messages to compute the short and longterm averages according to the process as described in FIG. 55. When theuser device ascertains that it is moving, the user sends an indicationor message 650 to the AP requesting to roam.

[0420] In FIG. 58 there is shown one mechanism that can be used by theprocessor in the implementations of either FIG. 56 or FIG. 57 tomaintain the short and long term averages needed to perform the processof FIG. 55 to ascertain movement. Two ring buffers 652 and 654 aremaintained—one for the short term average and one for the long termaverage. Ring buffers are used so that power sample averaging can beaccomplished over a sliding window in time. In a ring buffer, as a newsampled is added to the buffer, the oldest sample is removed. In thewireless networking example previously described, the short term averagering buffer stores the most recent 16 samples, and the long term averagering buffer stores on the order of 1024 or 2048 samples. Of course thesesample sizes will vary depending on the application. It may also bereasonable to use an accumulator-based average for the long termaverage, but such an approach could be subject to buffer overflow.

[0421] A short term average 656 and long term average 658 are calculatedbased on the contents of the respective ring buffers 652 and 654. Acomparator 660 uses a stored allowed range 662 and the short termaverage 556 and long term average 658 to produce the movement indication650 in accordance with the process of FIG. 55.

[0422] In FIG. 59 there is shown an alternate mechanism that can be usedby the processor in either FIG. 57 or FIG. 56 to maintain the short andlong term averages needed to perform the process of FIG. 55 to ascertainmovement. According to this mechanism, a ring buffer accumulates a smallnumber of samples, for example 16, for computation of the short termaverage. Each short term average computation is saved (656 a-656 n).After a certain number of short term averages have been computed andsaved, the long term average is computed as the average of all theaccumulated short term averages. This approach is known as “batchedmeans”. This approach is advantageous for use in systems containinglimited memory resources.

[0423] Though the above described aspects of the invention have beenexemplified as they apply to wireless networks and, in someparticularity, 802.11 networks, it will be clear to the skilledpractitioner that the invention can be employed in any wirelesscommunications environment, including wireless data networks, wirelessphone networks, and wireless I/O channels. All aspects of the inventionmay be implemented in either hardware or software. The preferredembodiment has been described as a software architecture because of itsadvantageous ease of portability between various hardware platforms.

[0424] It will be understood that each block of the flowchartillustrations, and combinations of blocks in the flowchartillustrations, can be implemented by computer program instructions.These computer program instructions may be loaded onto a computer,embedded device microprocessor (such as that found in an AP or STA), orother programmable data processing apparatus to produce a machine, suchthat the instructions which execute on the computer or otherprogrammable data processing apparatus create means for implementing thefunctions specified in the flowchart block or blocks. These computerprogram instructions may also be stored in a computer-readable memorythat can direct a computer or other programmable data processingapparatus to function in a particular manner, such that the instructionsstored in the computer-readable memory produce an article of manufactureincluding instruction means which implement the function specified inthe flowchart block or blocks. The computer program instructions mayalso be loaded onto a computer or other programmable data processingapparatus to cause a series of operational steps to be performed on thecomputer or other programmable apparatus to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide steps for implementingthe functions specified in the flowchart block or blocks.

[0425] Those skilled in the art should readily appreciate that programsdefining the functions of the present invention can be delivered to acomputer in many forms; including, but not limited to: (a) informationpermanently stored on non-writable storage media (e.g. read only memorydevices within a computer such as ROM or CD-ROM disks readable by acomputer I/O attachment); (b) information alterably stored on writablestorage media (e.g. floppy disks and hard drives); or (c) informationconveyed to a computer through communication media for example usingbaseband signaling or broadband signaling techniques, including carrierwave signaling techniques, such as over computer or telephone networksvia a modem.

[0426] While the invention is described through the above exemplaryembodiments, it will be understood by those of ordinary skill in the artthat modification to and variation of the illustrated embodiments may bemade without departing from the inventive concepts herein disclosed.Moreover, while the preferred embodiments are described in connectionwith various illustrative program command structures, one skilled in theart will recognize that the system may be embodied using a variety ofspecific command structures. Accordingly, the invention should not beviewed as limited except by the scope and spirit of the appended claims.

We claim:
 1. A method use by a wireless device in a wirelesscommunications environment, the method comprising the steps of:associating with a current access point; ascertaining whether thewireless device should attempt to associate with another access point;requesting association with the another access point if it isascertained that the wireless device should attempt to associate withsaid access point.
 2. The method of claim 1 further comprising the stepof: automatically collecting information about other access points. 3.The method of claim 2 wherein the step of ascertaining ascertains thatthe wireless device should attempt to associate with another accesspoint if the access point is closer than the current access point. 4.The method of claim 3 wherein the step of ascertaining ascertains thatthe access point is closer than the current access point by: calculatinga first biased distance between the wireless device and the currentaccess point based on “x” samples; calculating a second biased distancebetween the wireless device and the access point operating on saidanother channel based on “y” samples where “y” is less than “x”;Ascertaining that the access point operating on said another channel iscloser than the current access point if the second biased distance isless than the first biased distance.
 5. The method of claim 3 whereinthe step of requesting association requests association by sending amessage to the access point.